Abstract: ObjectiveTo understand the distribution of E.coli O157 animal hosts and the threats it brought.MethodsE.coli O157 was detected from 570 specimens which were collected from five farms in Chongqing city from June to September in 2001.Plasmid patterns and restriction endonuclease patterns were undertaken to illustrate the epidemiological relationship between strains.ResultsSeventeen strains E.coli O157 were isolated from feces and sew age specimens,and total isolaiton rates was about 2.89%.Three strains belong to O157:NM,the others were O157:H7.Two strains with completelyidentical plasmid patterns and restriction endonuclease patterns belonged to a single clone strain.Most results of PCR-VT2 PCR-hly vero-toxin tests were negetive,but were of haemolytic activity most of E.coli were with genes of eae and hly which had haemolytic activity and could cause expeimental rats dead.ConclusionThere were 2 types of E.coli O157 in Chongqing City.E.coli O157 strains isolated in Chongqing City were of their own characteristics,and there may be some more factors involved in virulence of E.coli O157.Pathogeny sheded by animal contaminated sur roundings,which threatened public health.