Abstract: The aim of the present study was to investigate the in vitro antibacterial activity of Mesona chinensis Benth.-containing serum in combination with antimicrobial agents on fos A3 gene-carrying and CTX-M-producing Escherichia coli（E. coli）. Twofold broth micro-dilution method was used to determine the minimum inhibitory concentration（MIC） of the selected antimicrobial agents and Mesona chinensis Benth.-containing serum against the E. coli strain separately; furthermore, the Mesona chinensis Benth.-containing serum of subinhibitory concentration（1/2 MIC） and antimicrobial agents were co-incubated with the E. coli strain to observe the co-inhibitory effect. The results showed that the combined application of Mesona chinensis Benth.-containing serum and antimicrobial agents had antibacterial activity against the fos A3 gene-carrying and CTX-M-producing E.coli strain, and the inhibitory effects of the selected antibacterial agents including aminoglycosides, alkaloids, polyphosphates,leflunomycin and sulfonamides against the drug resistant E. coli were strengthened by Mesona chinensis Benth..