In this study, 26 Streptococcus thermophilus phages were classified according to their structural protein patterns and DNA restriction fragment length polymorphism. Furthermore, sensitivities of natural and commercial S.thermophilus strains to S.thermophilus phages were investigated. All the natural strains were found to be resistant to the phages. The electrophoretic profiles of the structural proteins of S.thermophilus phages were identified according to the two common major bands at 30.6 and 27.3kDa. Various restriction endonucleases were used to digest S.thermophilus phages that were differentiated into eight subgroups depending on the length of EcoRV digestion. A phylogenetic tree was designed using fragments of EcoRV digestion. The results showed that all phages derived from a common ancestor and some of them were differentiated from each other over time.