Abstract: In order to study yak-diarrhea-derived Escherichia coli O antigen serotype and the carriage of high-pathogenitility island（HPI）-related genes, in the experiment, bacterial isolation and identification on 80 anal swab samples of diarrheic yaks taken from a yak farm in Shannan area, Tibet city. The isolated E. coli strains were also tested for F17 virulence factor O serotype identification and HPI-related genes irp3, irp5, irp2, ybtA, fyuA, irp8, ans-tRNA-intB. The results showed that a total of 28 suspected E. coli strains were isolated from 80 anal swab samples. Among the 28 isolates, five strains carried F17 virulence factor, with a total of 17 O antigen serotypes. Among them, O158 had the highest detection rate of 50.00%（14/28）; O125, O119, and O146 had high detection rates of 39.28%（11/28）, 39.28%（11/28）, and 35.71%（10/28）, respectively; while the number of strains of O127 and O18 had the lowest detection rate, both of which were 14.29%（4/28）. The positive rates of HPI-related genes irp3, irp5, irp2, ybtA, fyuA, irp8, ans-tRNA-intB were 35.71%（10/28）, 28.57%（8/28）, 32.14%（9/28）, 32.14%（9/28）, 28.57%（8/28）, 28.57%（8/28） and 28.57%（8/28）, respectively. The results indicated that the dominant serotype of isolated yak-diarrhea-derived E. coli was O158 and there was HPI related genes were carried.