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 breast cancer. Materials and Methods: A total of 40 Formalin fixed paraffin embedded samples with diagnosis of breast cancer were collected in a period of 3 years from cancer institute of Iran. We selected both pre-menopausal and post-menopausal patients with different histologic grades and different ethnic groups. We evaluated presence of MMTV-like virus env gene through real time PCR method. Results: Forty patients (20 pre and 20 postmenopausal women) were evaluated with the mean age of 49.67. The average tumor size was 39 mm. None of the studied samples were positive for MMTV-like virus env gene target sequences. Conclusions: We found no evidence on the potential role of MMTV-like virus in the carcinogenicity of breast cancer among Iranian women.