diff --git a/src/mipscpu.cpp b/src/mipscpu.cpp
index 3b0f54b..2932972 100644
--- a/src/mipscpu.cpp
+++ b/src/mipscpu.cpp
@@ -78,6 +78,7 @@ namespace tememu
         REG_OP_FUNC(op_or,      0x25 << 4);
         REG_OP_FUNC(op_ori,     0x0D);
         REG_OP_FUNC(op_xor,     0x26 << 4);
+        REG_OP_FUNC(op_nor,     0x27 << 4);
     }
 
     void MipsCPU::reset()
@@ -297,6 +298,12 @@ namespace tememu
         step();
     }
 
+    void MipsCPU::op_nor(int32 instr)
+    {
+        _GPR[RD(instr)] = ~(_GPR[RS(instr)] | _GPR[RT(instr)]);
+        step();
+    }
+
     void MipsCPU::loadProgram(boost::shared_ptr< std::vector<int32> > program)
     {
         _program = program;
diff --git a/src/mipscpu.h b/src/mipscpu.h
index d794f9d..a65f3f7 100644
--- a/src/mipscpu.h
+++ b/src/mipscpu.h
@@ -108,6 +108,7 @@ namespace tememu
         void op_or(int32);
         void op_ori(int32);
         void op_xor(int32);
+        void op_nor(int32);
     
     private:
         std::vector<int32> _GPR, _FPR, _FCR;
diff --git a/test/main.cpp b/test/main.cpp
index a3f5c97..24faa60 100644
--- a/test/main.cpp
+++ b/test/main.cpp
@@ -596,3 +596,32 @@ TEST(Logical, op_xor)
     cpu.runProgram();
     EXPECT_EQ(cpu.gprValue(7), 0x0ff00ff0);
 }
+
+TEST(Logical, op_nor)
+{
+    tememu::MipsCPU cpu;
+    boost::shared_ptr< std::vector<int32> > program(new std::vector<int32>);
+
+    program->push_back(0x00a63827); // xor $a3, $a1, $a2
+    cpu.loadProgram(program);
+
+    cpu.setGPR(5, 0xffffffff);
+    cpu.setGPR(6, 0);
+    cpu.runProgram();
+    EXPECT_EQ(cpu.gprValue(7), 0);
+
+    cpu.reset();
+
+    cpu.setGPR(5, 0x0000ffff);
+    cpu.setGPR(6, 0xfffff000);
+    cpu.runProgram();
+    EXPECT_EQ(cpu.gprValue(7), 0);
+
+    cpu.reset(); 
+
+    cpu.setGPR(5, 0xff00ff00);
+    cpu.setGPR(6, 0xf0f0f0f0);
+    cpu.runProgram();
+    EXPECT_EQ(cpu.gprValue(7), 0x000f000f);
+}
+