Waste oil refinery catalyst from the FCC unit was tested as a possible additive for the production of polymeric composites with antimicrobial properties. The effect of the silver ion on the growth inhibition of bacteria (E. coli and S. aureus), mold (A. niger), and yeasts (C. tropicalis and Cr. humicolus) was studied. The catalyst was ion exchanged with silver nitrate and incorporated into thermoplastic polyurethanes with different hardness ratings. The materials produced were submitted to microbial testing both in solid and liquid media, and the effect of the polymeric matrix on the rate of silver ion release from these materials was also investigated. The results obtained show that polyurethane composite containing the silver-ion-exchanged waste catalyst successfully inhibited the growth of all microorganisms under study.