A total of one hundred and thirty random milk and some milk products samples were collected from different markets, and were examined for the presence of Escherichia coli O157:H7. The organism could be isolated from one sample (2%) of each of milk and cheese samples, but it failed to detect in yoghurt samples. An important cause of haemolytic anaemia syndrome and lethal effect on mice was detected, while enterotoxin of strain gave maximum secretion in rabbit ligated ileal loop. Raw milk and milk products samples (cheese and yoghourt) free from  E. coli O157:H7 were inoculated by strain of E. coli O157:H7 obtained from a Bacteriology Veterinary Lab. The effects of irradiation on the inoculated milk and milk products stored at 8°C and 5°C were determined. As survivor level of E. coli O157:H7 following gamma irradiation appeared completely discarded in refrigerator on 1, 2 & 3 days of incubation at 5°C. The cytotoxin production was completely stopped by irradiation at 0.25-0.53 kgy.