diff --git a/include/instructions.h b/include/instructions.h
index 2ce183e..c7616b4 100644
--- a/include/instructions.h
+++ b/include/instructions.h
@@ -42,6 +42,7 @@ public:
   void xor_rm32_r32();  // 0x31
   void xor_r32_rm32();  // 0x33
   void xor_eax_imm32(); // 0x35
+  void cmp_rm32_r32();  // 0x39
   void inc_eax();       // 0x40
   void inc_ecx();       // 0x41
   void inc_edx();       // 0x42
diff --git a/instructions.cpp b/instructions.cpp
index 9855719..5018d21 100644
--- a/instructions.cpp
+++ b/instructions.cpp
@@ -35,6 +35,7 @@ void Instructions::init_instructions(){
   this->instructions[0x31] = &Instructions::xor_rm32_r32;
   this->instructions[0x33] = &Instructions::xor_r32_rm32;
   this->instructions[0x35] = &Instructions::xor_eax_imm32;
+  this->instructions[0x39] = &Instructions::cmp_rm32_r32;
   this->instructions[0x40] = &Instructions::inc_eax;
   this->instructions[0x41] = &Instructions::inc_ecx;
   this->instructions[0x42] = &Instructions::inc_edx;
@@ -640,6 +641,59 @@ void Instructions::xor_eax_imm32(){
   this->registers[0] ^= imm32;
 }
 
+void Instructions::cmp_rm32_r32(){
+  //printf("cmp_rm32_r32 called.\n");
+  uint32_t addr, dst, imm32, result;
+  uint8_t imm8;
+
+  this->modrm = memory.read_uint8(this->eip);
+  this->calc_modrm();
+
+  switch (this->mod) {
+    case 0:
+      // cmp [M], R
+      // addr : M
+      this->eip++;
+      addr = this->registers[this->M];
+      // dst : data of [M]
+      dst = memory.read_uint32(addr);
+      result = dst - this->registers[this->R];
+      set_flag(!result, ZF);
+      break;
+    case 1:
+      // cmp [M+imm8], R
+      this->eip++;
+      imm8 = memory.read_uint8(this->eip);
+      // addr : M
+      addr = this->registers[this->M];
+      // dst : data of [M+imm8]
+      dst = memory.read_uint32(addr + imm8);
+      result = dst - this->registers[this->R];
+      set_flag(!result, ZF);
+      break;
+    case 2:
+      // cmp [M+imm32], R
+      this->eip++;
+      imm32 = memory.read_uint32(this->eip);
+      imm32 = swap_endian32(imm32);
+      // addr : M
+      addr = this->registers[this->M];
+      // dst : data of [M+imm32]
+      dst = memory.read_uint32(addr + imm32);
+      result = dst - this->registers[this->R];
+      set_flag(!result, ZF);
+      this->eip += 4;
+      break;
+    default:
+      // case mod == 3
+      // cmp M, R
+      this->eip++;
+      result = this->registers[this->M] - this->registers[this->R];
+      set_flag(!result, ZF);
+      break;
+  }
+}
+
 void Instructions::inc_eax(){
   //printf("inc_eax called.\n");
   this->registers[0]++;