Nitriding of AISI 303 austenitic stainless steel using microwave plasma system at various temperatures was conducted in the present study. The nitrided layers were characterized via scanning electron microscopy, glancing angle X-ray diffraction, transmission electron microscopy and Vickers microhardness tester. The antibacterial properties of this nitrided layer were evaluated. During nitriding treatment between 350 degrees C and 550 degrees C, the phase transformation sequence on the nitrided layers of the alloys was found to be gamma ->(gamma+gamma(N))->(gamma+alpha+CrN). The analytical results revealed that the surface hardness of AISI 303 stainless steel could be enhanced with the formation of gamma(N) phase in nitriding process. Antibacterial test also demonstrated the nitrided layer processed the excellent antibacterial properties. The enhanced surface hardness and antibacterial properties make the nitrided AISI 303 austenitic stainless steel to be one of the essential materials in the biomedical applications. (C) 2011 Elsevier B. V. All rights reserved.