Escherichia coli O157 is a food-borne pathogen that attributed to the contamination of some sea foods including fish and shellfish. This study was aimed to identification of Escherichia coli in some marine fish and shellfish such as, lobster, crab and shrimp, and to investigate the occurrence of Escherichia coli O157 as a food born bacterial pathogen. The study was carried out in Isfahan markets (Iran) during spring and summer 2011. A total of 190 samples (90 fish, 40 lobster, 30 shrimp and 30 crabs) were collected, Samples were randomly obtained from the fish markets and examined based on their growth characteristics on specific culture media and molecular (PCR) tests. Among all samples, 49 cases (25.78%) contaminated by E.coli, that among these isolates two cases were distinguished as an E.coli O157. In these samples E.coli O157:H7 was not identified. The highest and lowest contamination rate was observed among fishes and crab with 34.44 and 10 percents, respectively. Also the contamination rates of E.coli in different seasons were 15.78 and 10 percent in spring and summer, respectively. It can be concluded that marine fish and shellfish can carry some pathogenic bacteria as E.coli O:157 that have risks for human health.