Abstract: The purpose of this study was to evaluate the antibacterial effects of 16 Mongolian herb medicines on pathogenic Escherichia coli （E. coli） of 3 different serotypes in vitro. The inhibition diameters of the Mongolian herb medicines against the tested strains were determined by Oxford cup method; the minimal inhibitory concentration （MIC） and minimum bactericidal concentration （MBC） were determined using micro-dilution method in combination with agar plate method; the fractional inhibitory concentration indexes（FICI） of the screened Mongolian herb medicines with superior antibacterial activity were determined by chessboard method. The results showed that the inhibition diameters of Urishgu-Dalan-Harrisu, Syner-Honglian and Ullajigana against the E. coli of 3 different serotypes ranged from 16.10 mm to 29.64 mm,the corresponding MIC ranged from 7.81 mg/mL to 31.25 mg/mL,and the corresponding MBC ranged from 15.63 mg/mL to 125 mg/mL; the FICI of Ullajigana and Syner-Honglian as well as Schubugri-Himuledeg and Hur-Turu against E. coli O26 were both 0.50; the FICI of Ullajigana and Urishgu-Dalan-Harrisu against E. coli O83 was 0.50. The combined data suggested that Urishgu-Dalan-Harrisu, Syner-Honglian, Hur-Turu, Ullajigana and Anar had a better performance in comprehensive bacteriostasis effect against E. coli of 3 serotypes; Schubugri-Himuledeg and Hur-Turu exhibited a synergistic effect in inhibiting E. coli O26, which could be given priority in the formulation; Ullajigana and Urishgu-Dalan-Harrisu expressed a synergistic effect in inhibiting E. coli O83, which could be given priority in the formulation.