In this study, antibacterial activities of Propycil (R) which is a antithyroid drug were examined for its antibacterial activity against test bacteria and its potencial mutagenic activity on organism. Antibacterial activity were tested against Staphylococcus aureus ATCC 6538, Pseudomonas aeruginosa ATCC 9027, Bacillus megaterium DSM 32, and Enterobacter aerogenes, Escherichia coli, Klebsiella pneumoniae which are clinic isolates. Potencial mutagenic activity of Propycil (R) were tested in TA 98 and TA 100 strains of Salmonella typhimurium using Ames test. Consequently, it was observed that Propycil (R) was caused inhbition zones on Klebsiella pneumoniae 13,35 mm ye Pseudomonas aeruginosa ATCC 9027 15,46 mm. In the Ames test, while none of the doses tested caused frame shift mutations on TA 98 strains, all other doses, except for the highest dose, was determined to cause a base pair substitution mutation change on TA 100 strains.