Abstract: Objective To study the biological characteristics of EHEC O157:H7 and other E.coli O157 (hereinafter called as O157: non-H7) so as to establish highly efficient and practical O157:H7 isolation procedure as well as identification index. Methods Biochemical test and slide agglutination test were used respectively to determine the biological characteristics and O antigen of strains; Antiserum agar inoculated with anti-H7 by puncture was used to detect H7 flagellar antigen and tube agglutination test was adopted to determine other flagelar antigen. Polymerase Chain Reaction (PCR) was used to test specific genes and toxici-ty genes,respectively. Results 194 strains of O157:H7 and 101 strains of O157:non-H7 had differences in biochemical reaction including sorbitol,sucrose, lysine and ornthine,etc. 192 strains of the total 194(98.97%) carried O157 specific gene and 189 strains (97.42%) had positive antigen phenotype;101 strains of O157:H7 all carried O157 specific gene and the phenotype was positive simultaneously. 194 strains of O157:H7 all carried H7 specific gene and the flagellar antigen of 186 strains (9588%) was positive. Except one within 194 strains of 0157:H7 had negative results of 4 toxicity genes,the other 193 strains all carried 2 or more toxicity genes;the testing of 4 toxicity genes in 101 strains of O157:non-H7 were all negative. Con-clusion The characteristic biochemical reaction of O157:H7,determination of O157 and H7 specific genes as well as the feature of toxicity genes had a great impotrance in differentiating O157 of various types,on the ba-sis of which highly pertinent O157:H7 isolation and identification procedure would be established.