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Introduction: Staphylococcus pseudintermedius, a bacterium considered part of the normal flora in dogs, poses a serious threat to the canine health system because it carries a large assortment of pathogenicity and virulence genes, which allow it to be capable of developing multi-drug resistance. 1 However, no long-term studies have examined the evolutionary history of MRSP’s resistance to antibiotics. Objective: The research project sought to phenotypically characterize historical MRSP environmental and canine isolates collected from The Ohio State University Veterinary Medical Center from 2007 to 2013. Results: Linear regression analysis showed that MRSP resistance increased significantly, by approximately one new class of antibiotic every 5 years, in environmental isolates pooled across all hospital locations. MRSP resistance did not increase significantly over time for canine isolates. Conclusions: MRSP appears to have increased its resistance to different classes of antimicrobial drugs over the past 6 years, suggesting that MRSP is continuing to acquire novel genetic components and become even more pathogenic. Researchers now need to focus on preventive measures that will deter or slow this process.