Phages are the most important natural antimicrobial agents. They have some important advantages in comparison with other chemical antibiotics. Escherichia coli (E. coli) as a Gram-negative bacteria belongs to the Enterobacteriaceae family. E. coli O157 as the most well-known member of this family is the cause of some diseases and food poisonings. Symptoms of infection with these bacteria are mild to severe bloody diarrhea and even death. Researches in recent years prove the existence of multidrug resistant strains of bacteria. Phages can be an alternative antibiotic agent for treatment against resistant bacteria that can cause serious problems. The most difficult step in the development of phage drugs for the purpose of treatment is isolation and purification of strong phages. In this article we tried to isolate coliphages from environmental samples like waste water and simple and manure enriched soil. Phage isolation and purification steps of environmental samples and wastewater were performed according to plaque and spot assay methods. Eventually we isolated a phage belongs to the siphoviridae family that specificly destroys E. coli O157. It can be used be an agent for treatment E. coli O157 infections with nearly no side effects.