Background: Mouse mammary tumor virus (MMTV) is the major cause of mammary tumors in mice.There is limited controversial evidence about the probable etiologic role of MMTV- like virus in human breastcancer. Materials and Methods: A total of 40 Formalin fixed paraffin embedded samples with diagnosis of breastcancer were collected in a period of 3 years from cancer institute of Iran. We selected both pre-menopausal andpost-menopausal patients with different histologic grades and different ethnic groups. We evaluated presenceof MMTV-like virus env gene through real time PCR method. Results: Forty patients (20 pre and 20 postmenopausalwomen) were evaluated with the mean age of 49.67. The average tumor size was 39 mm. None ofthe studied samples were positive for MMTV-like virus env gene target sequences. Conclusions: We found noevidence on the potential role of MMTV-like virus in the carcinogenicity of breast cancer among Iranian women.