Abstract: ObjectiveThe in vitro antibacterial effect of water extract from Epimedium brevicornu Maxim. combined with antimicrobials on drug-resistant Escherichia coli was studied,in order to provide reference basis for combination of traditional Chinese and western medicines in veterinary clinic , also lay foundation for development and research of tradi-tional Chinese medicine against drug-resistant strains. MethodThe microbroth dilution assay methods were used to de-termine minimal inhibitory concentration (MIC) of water extract from E. brevicornu and antimicrobials against extended spectrum beta-lactamases(ESBLs)-producing E. coli. Then their fractional inhibitory concentration index(FICI) was de-termined with microdilution checkerboard techniques . ResultAfter combining antimicrobials with water extract of E. brevicornu, the MICs of colistin, ceftriaxone sodium, ceftazidime, ceftiofur, amoxicillin, fosfomycin, amikacin, florfeni-col, maquindox, clindamycin were decreased more than four times, the FICIs were 0.13, 0.26, 0.26, 0.25, 0.51, 0.51, 0.50, 0.75, 0.75 and 0.75, so water extract from E. brevicornu combined with antimicrobials showed synergistic or additive inhibitory effect on ESBLs-producing E. coli. Furthermore, after water extract from E. brevicornu combined with antimi-crobials were used to induce passage of ESBLs-producing E. coli, it was found that medicine combination could signifi-cantly reduce the MICs of antibiotics from the 1st generation to the 3rd generation. ConclusionThe combination of water extract from E. brevicornu with colistin, ceftriaxone sodium, ceftazidime, ceftiofur, amoxicillin, fosfomycin, amikacin, florfenicol, maquindox, clindamycin can improve inhibitory effect on ESBLs-producing E. coli by their synergistic or ad-ditive effect, but is inadvisable to combine with sulfa and quinolone.