ObjectiveTo explore stability of in vitro activity of vancomycin and fidaxomicin against Clostridium difficile (C. difficile).MethodsMultistep induction method was used to perform in vitro induction testing on 15 strains of clinically isolated C.difficile (2 were ribotype HB1/RT001，3 were HB5/RT017，3 were HB6/RT012，3 were HB3，1 was HB24，and 3 were HB25）and 5 standard C.difficile strains（ATCC 700057, ATCC 1382, ATCC 9689, ATCC 43598, and ATCC 1870）, after theses strains were passaged for 20 times on modified Brucella blood agar plate containing vancomycin and fidaxomicin of 1/2 fold minimum inhibitory concentration(MIC) and 1 fold MIC respectively, MICs before and after induction were determined by agar dilution method.ResultsMICs of vancomycin against all strains before induction were 0.125-0.50 μg/mL, after strains were passaged for 20 times, MICs were 0.50-2.00 μg/mL, MICs of 3 strains increased 4fold, 13 strains increased 2fold. MICs of fidaxomicin against all strains before and after induction were 0.015-0.50 μg/mL and 0.0075-0.50 μg/mL respectively，MICs of 3 strains increased 8fold, 4 strains increased 4fold.ConclusionVancomycin and amphotericin have good stability for in vitro activity against C.difficile, secondary drug resistance is not easy to produce.