In this study a total of 120 diarrheic buffalo calves were examined clinically and bacteriologically was investigated. The role of E. coli in diarrheic buffalo calves. E. coli, could be isolated from 31 (25.80%) calves. K99 antigen could be detected in (12.90%) isolates. Studying some virulence factors of E. coli isolates revealed that 28 (90.30) isolates showed congored binding, 29 (93.50%) isolates were able to survive in serum and 23 (74.19%) were able to grow in calf serum, 25 (80.64 %) isolates could be proved as enterotoxin producers and caused accumulation of fluids in the intestinal tract of the inoculated mice. In addition, 28 (90.30 %) were able to produce verotoxins. The present study demonstrated the correlation between the presence of different virulence factors in E. coli isolates and its pathogenicity to newborn calves and its role in diarrheic calves