This study investigated the mechanisms of resistance of 36 quinolone-resistant Salmonella Typhimurium strains isolated from outpatients with infectious diarrhea in Beijing Tian Tan Hospital between 2013 and 2015. The resistance spectrum of the 36 strains was measured using a broth dilution method. Class 1 integrons harboring the β-lactamase gene and mutations in quinolone resistance determining regions were also investigated. All 36 quinolone-resistant Salmonella Typhimurium strains were found to be multidrug-resistant and the majority of these strains harbored Class 1 integrons. These findings study suggests that strategies for determining resistance spectrums should be implemented with greater urgency.