Abstract: The cell-bound penicillinase and exopenicillinase were excreted by the S. aurcus75 strain isolated clinically in Nanjing, but no cell-bound exopenicillinase was demonstrated. When the exponentially growing cultures were induced by adding oxacillin alone, penicillinase produced was at a low rate in the cultures. However, if sodium citrate is placed in the culture medium before, the prduction of the penicillinase by oxacillin was increasd in a large amount in the cultures. When the concentration of the sodium citrate in the medium was 0. 15M the specific activity of the total penicillinase and the exopenicillinase in the cultures over a period of 18 hrs. was about 8.7 and 16.9 fold respectively as much as that in control.The staphylococcal exopenici1linase was purified by the modified Richmond's method, the total recovery being 25.33% and the specific activity being 2l729units/μg of protein.