diff --git a/Core/Debugger.cpp b/Core/Debugger.cpp
index 346c5224..63dea80b 100644
--- a/Core/Debugger.cpp
+++ b/Core/Debugger.cpp
@@ -79,7 +79,11 @@ void Debugger::Resume()
 
 void Debugger::SetFlags(uint32_t flags)
 {
+	bool needUpdate = ((flags ^ _flags) & (int)DebuggerFlags::DisplayOpCodesInLowerCase) != 0;
 	_flags = flags;
+	if(needUpdate) {
+		_disassembler->BuildOpCodeTables(CheckFlag(DebuggerFlags::DisplayOpCodesInLowerCase));
+	}
 }
 
 bool Debugger::CheckFlag(DebuggerFlags flag)
diff --git a/Core/DebuggerTypes.h b/Core/DebuggerTypes.h
index 85918f85..556b3fab 100644
--- a/Core/DebuggerTypes.h
+++ b/Core/DebuggerTypes.h
@@ -4,7 +4,8 @@ enum class DebuggerFlags
 {
 	PpuPartialDraw = 1,
 	ShowEffectiveAddresses = 2,
-	ShowOnlyDisassembledCode = 4
+	ShowOnlyDisassembledCode = 4,
+	DisplayOpCodesInLowerCase = 8
 };
 
 enum class AddressType
diff --git a/Core/Disassembler.cpp b/Core/Disassembler.cpp
index ea2a9896..239fa3a0 100644
--- a/Core/Disassembler.cpp
+++ b/Core/Disassembler.cpp
@@ -25,6 +25,15 @@ Disassembler::Disassembler(uint8_t* internalRam, uint8_t* prgRom, uint32_t prgSi
 		_disassembleMemoryCache.push_back(shared_ptr<DisassemblyInfo>(nullptr));
 	}
 
+	BuildOpCodeTables(false);
+}
+
+Disassembler::~Disassembler()
+{
+}
+
+void Disassembler::BuildOpCodeTables(bool useLowerCase)
+{
 	string opName[256] = {
 	//	0			1			2			3			4			5			6			7			8			9			A			B			C			D			E			F
 		"BRK",	"ORA",	"",		"SLO*",	"NOP",	"ORA",	"ASL",	"SLO*",	"PHP",	"ORA",	"ASL",	"ANC*",	"NOP",	"ORA",	"ASL",	"SLO*", //0
@@ -65,7 +74,14 @@ Disassembler::Disassembler(uint8_t* internalRam, uint8_t* prgRom, uint32_t prgSi
 	};
 
 	for(int i = 0; i < 256; i++) {
-		DisassemblyInfo::OPName[i] = opName[i];
+		if(useLowerCase) {
+			string name = opName[i];
+			std::transform(name.begin(), name.end(), name.begin(), std::tolower);
+			DisassemblyInfo::OPName[i] = name;
+		} else {
+			DisassemblyInfo::OPName[i] = opName[i];
+		}
+
 		DisassemblyInfo::OPMode[i] = opMode[i];
 		switch(DisassemblyInfo::OPMode[i]) {
 			case AddrMode::Abs:
@@ -95,10 +111,6 @@ Disassembler::Disassembler(uint8_t* internalRam, uint8_t* prgRom, uint32_t prgSi
 	}
 }
 
-Disassembler::~Disassembler()
-{
-}
-
 bool Disassembler::IsJump(uint8_t opCode)
 {
 	return opCode == 0x10 || opCode == 0x30|| opCode == 0x50 || opCode == 0x70 || opCode == 0x90 || opCode == 0xB0 || opCode == 0xD0 || opCode == 0xF0 || opCode == 0x4C || opCode == 0x20;
diff --git a/Core/Disassembler.h b/Core/Disassembler.h
index 48b0faf6..46e32d8c 100644
--- a/Core/Disassembler.h
+++ b/Core/Disassembler.h
@@ -29,6 +29,8 @@ private:
 public:
 	Disassembler(uint8_t* internalRam, uint8_t* prgRom, uint32_t prgSize, uint8_t* prgRam, uint32_t prgRamSize, Debugger* debugger);
 	~Disassembler();
+
+	void BuildOpCodeTables(bool useLowerCase);
 	
 	uint32_t BuildCache(int32_t absoluteAddr, int32_t absoluteRamAddr, uint16_t memoryAddr, bool isSubEntryPoint);
 	void InvalidateCache(uint16_t memoryAddr, int32_t absoluteRamAddr);
diff --git a/GUI.NET/Config/DebugInfo.cs b/GUI.NET/Config/DebugInfo.cs
index 6376aac7..5fa1b8d2 100644
--- a/GUI.NET/Config/DebugInfo.cs
+++ b/GUI.NET/Config/DebugInfo.cs
@@ -74,6 +74,7 @@ namespace Mesen.GUI.Config
 
 		public bool SplitView = false;
 		public bool HexDisplay = true;
+		public bool DisplayOpCodesInLowerCase = false;
 
 		public bool PpuAutoRefresh = true;
 		public bool PpuPartialDraw = false;
diff --git a/GUI.NET/Debugger/frmDebugger.Designer.cs b/GUI.NET/Debugger/frmDebugger.Designer.cs
index da3d01f4..ba53031b 100644
--- a/GUI.NET/Debugger/frmDebugger.Designer.cs
+++ b/GUI.NET/Debugger/frmDebugger.Designer.cs
@@ -127,6 +127,7 @@
 			this.lblChrAnalysisResult = new System.Windows.Forms.ToolStripStatusLabel();
 			this.ctrlPpuMemoryMapping = new Mesen.GUI.Debugger.Controls.ctrlMemoryMapping();
 			this.ctrlCpuMemoryMapping = new Mesen.GUI.Debugger.Controls.ctrlMemoryMapping();
+			this.mnuDisplayOpCodesInLowerCase = new System.Windows.Forms.ToolStripMenuItem();
 			((System.ComponentModel.ISupportInitialize)(this.splitContainer)).BeginInit();
 			this.splitContainer.Panel1.SuspendLayout();
 			this.splitContainer.Panel2.SuspendLayout();
@@ -680,6 +681,7 @@
 			this.mnuOptions.DropDownItems.AddRange(new System.Windows.Forms.ToolStripItem[] {
             this.mnuSplitView,
             this.fontSizeToolStripMenuItem,
+            this.mnuDisplayOpCodesInLowerCase,
             this.toolStripMenuItem5,
             this.mnuBreakOnReset,
             this.mnuBreakOnOpen,
@@ -996,6 +998,14 @@
 			this.ctrlCpuMemoryMapping.Text = "ctrlMemoryMapping1";
 			this.ctrlCpuMemoryMapping.Visible = false;
 			// 
+			// mnuDisplayOpCodesInLowerCase
+			// 
+			this.mnuDisplayOpCodesInLowerCase.CheckOnClick = true;
+			this.mnuDisplayOpCodesInLowerCase.Name = "mnuDisplayOpCodesInLowerCase";
+			this.mnuDisplayOpCodesInLowerCase.Size = new System.Drawing.Size(243, 22);
+			this.mnuDisplayOpCodesInLowerCase.Text = "Display OP codes in lower case";
+			this.mnuDisplayOpCodesInLowerCase.Click += new System.EventHandler(this.mnuDisplayOpCodesInLowerCase_Click);
+			// 
 			// frmDebugger
 			// 
 			this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
@@ -1130,5 +1140,6 @@
 		private System.Windows.Forms.ToolStripSeparator toolStripMenuItem11;
 		private System.Windows.Forms.ToolStripMenuItem mnuDisableDefaultLabels;
 		private System.Windows.Forms.ToolStripMenuItem mnuBreakOnReset;
+		private System.Windows.Forms.ToolStripMenuItem mnuDisplayOpCodesInLowerCase;
 	}
 }
\ No newline at end of file
diff --git a/GUI.NET/Debugger/frmDebugger.cs b/GUI.NET/Debugger/frmDebugger.cs
index 00d2a56c..84d27b49 100644
--- a/GUI.NET/Debugger/frmDebugger.cs
+++ b/GUI.NET/Debugger/frmDebugger.cs
@@ -51,6 +51,7 @@ namespace Mesen.GUI.Debugger
 			this.mnuHighlightUnexecutedCode.Checked = ConfigManager.Config.DebugInfo.HighlightUnexecutedCode;
 			this.mnuAutoLoadDbgFiles.Checked = ConfigManager.Config.DebugInfo.AutoLoadDbgFiles;
 			this.mnuBreakOnOpen.Checked = ConfigManager.Config.DebugInfo.BreakOnOpen;
+			this.mnuDisplayOpCodesInLowerCase.Checked = ConfigManager.Config.DebugInfo.DisplayOpCodesInLowerCase;
 
 			ctrlCpuMemoryMapping.Visible = mnuShowCpuMemoryMapping.Checked;
 			ctrlPpuMemoryMapping.Visible = mnuShowPpuMemoryMapping.Checked;
@@ -172,6 +173,9 @@ namespace Mesen.GUI.Debugger
 			if(mnuShowOnlyDisassembledCode.Checked) {
 				flags |= DebuggerFlags.ShowOnlyDisassembledCode;
 			}
+			if(mnuDisplayOpCodesInLowerCase.Checked) {
+				flags |= DebuggerFlags.DisplayOpCodesInLowerCase;
+			}
 			InteropEmu.DebugSetFlags(flags);
 		}
 
@@ -621,6 +625,14 @@ namespace Mesen.GUI.Debugger
 			ConfigManager.ApplyChanges();
 		}
 
+		private void mnuDisplayOpCodesInLowerCase_Click(object sender, EventArgs e)
+		{
+			ConfigManager.Config.DebugInfo.DisplayOpCodesInLowerCase = mnuDisplayOpCodesInLowerCase.Checked;
+			ConfigManager.ApplyChanges();
+			this.UpdateDebuggerFlags();
+			this.UpdateDebugger(false);
+		}
+
 		private void frmDebugger_Resize(object sender, EventArgs e)
 		{
 			ctrlCpuMemoryMapping.Invalidate();
@@ -655,7 +667,7 @@ namespace Mesen.GUI.Debugger
 				_workspace = null;
 				LabelManager.ResetLabels();
 				UpdateWorkspace();
-				UpdateDebugger();
+				UpdateDebugger(false);
 			}
 		}
 
diff --git a/GUI.NET/InteropEmu.cs b/GUI.NET/InteropEmu.cs
index f034c1fb..209ff083 100644
--- a/GUI.NET/InteropEmu.cs
+++ b/GUI.NET/InteropEmu.cs
@@ -816,6 +816,7 @@ namespace Mesen.GUI
 		PpuPartialDraw = 1,
 		ShowEffectiveAddresses = 2,
 		ShowOnlyDisassembledCode = 4,
+		DisplayOpCodesInLowerCase = 8,
 	}
 
 	public struct InteropRomInfo