By applying solution nitriding to conventional martensitic stainless steel of SUS410. we could produce high nitrogen martensitic stainless steel successfully. Firstly, the hardness and microstrucnire of the martensitic stainless steel obtained was investigated for the as-solution-nitrided specimen without tempering. After tliat, the change in hardness with tempering was investigated as well as microstructure. The results obtained were summarized as follows: (1) SUS410 added nitrogen by solution nitriding at M73K.-0.lMPa contained about 0.3mass% nitrogen. (2) The increase in the hardness of SUS410 solution-nitrided rose about l.OGPa. However, hardening effect by nitrogen was significantly smaller than that by carbon. (3) There was no effect of solution nitriding on microstructure of SUS410. (4) Because of the precipitation of very fine CrN nitrides, the maximum hardness obtained in the 773K tempered SUS410-0.3N reached 6.9GPa which was the same harness as that of the as-quenched SUS420J2.