A new nickel-free austenitic stainless steel, named BIOSSN4, has been recently developed to avoid the sensitivity to Ni ions. In the present study, the blood compatibility of the nickel-free stainless steel was evaluated in vitro by the platelet-rich plasma adhesion test with comparison to 316L stainless steel. The result shows that the nickel-free stainless steel only causes less activation of platelets, which was indicated by their morphology and low spreading. The result suggests that the nickel-free stainless steel should have better blood compatibility compared with 316L stainless steel and, as a bio-material, it should have obvious advantage and potential applications.