Diarrhea is an important problem in young calves, especially in suckling beef calves. The mostcommon cause of diarrhea in calves is E.coli. The present study was undertaken to screen  for presence of virulence factors associated with colibacillosis isolated from one hundred and twenty five fecal samples of calves suffer from diarrhea (<3monthes). All samples were submitted for bacteriological examination, serotyping and virulence tests (Congo red test, serum resistant test, sereny test and haemolytic activity). Finally molecular Identification by using Polymerase chain reaction (PCR) to detect shiga toxin (stx1, stx2) genes. E.coli isolates were fifty eight isolates (46.4%). The fecal samples were obtained a Twelve different serotype of E.coli (O26:H11, O91:H21, O103:H2, O111:H2, O15:H21, O146:H21, O8,O113:H4, O128:H2, O124, O121:H7 and O55:H7). It was recorded forty two isolates (72.4%) were congo red positive, forty two isolates (72.4%) were serum resistant, eleven isolates (18.96%) made keratoconjunctivitis of Guinea pig and fourteen isolates (24.13%) had hemolytic activity. PCR was performed to detect stx1 and stx2 genes on different serotypes of E.coli isolates. The serotypes which positive to stx1 gene only were three (O8,O113:H4,O128:H2) (30%), two serotypes were positive to stx2 only (O15:H21,O146:H21) (20%), four serotypes were positive to both stx1 and stx2 (O26:H11, O91:H21, O103:H2,O111:H2) (40%) and O124 was negative for both stx1 and stx2(10%). This result of E.coli strains isolated from diarrheic calves implies that these animals are an important reservoir of Shiga toxin Escherichia coli (STEC) strains that are potentially pathogenic toward farm animals.