Some Factors determining the virulence of Escherichia coli ( E. coli ) isolates were studied ,of 25 isolates , 17(group A) uropathogenic E. coli ,6 (group B) infected gastrointestinal tract , 2 (group C) infected wound , beside these group we use the standard strain E. coli HB101 as control group. The twenty five isolates were tested for adherence capability to human buccal cavity epithelial cells by in vitro experiment . The results showed that all isolates have different adhesion capability with mean ranging from (14.35±11.39) to (33.80 ± 22.68) bacteria / epithelial cell It was noticed that isolates EU9, ES6, EW17 displayed high adhesive capability with mean value (33.80 ± 22.68), (32.60 ± 21.19), (29.90±22.50) bacteria /epithelial cell respectively, while the isolates EU4 displayed a lowest adhesive capability with mean value of (14.35±11.39) bacteria / epithelial cell. It was also found that there was no significant difference ( P ≥ 0.001) for adhesive capability among EU9, ES6, EW17, but the adhesive capability for these isolates was significantly higher (P ≤ 0.001) compared to standard strain which showed adhesive capability with mean value (0.55± 0.88),thus these isolates were selected for further experiments to study others virulence factors such as ability to agglutination human , rabbit , sheep erythrocytes in mannose – sensitive manner and production of haemolysin , biofilm. The results revealed that all isolates had nearly the same hemagluttination pattern in the absence of D-mannose while the pattern is different in the presence of D- mannose, where the isolates EU9, ES6 show ability to agglutinate human and sheep erythrocytes and so considered as Mannose Resistant Hemagluttination (MRHA) while the isolate EW17 did not show this ability and considered as Mannose Sensitive Hemagluttination ( MSHA). It was also found that all isolates have ability to produce haemolysin and biofilm formation but in different pattern.