Breast cancer is the most common cancer among women worldwide. Roles of the Epstein-Barr, Merkelcell polyoma and mouse mammary tumor viruses in breast carcinogenesis are still controversial although anyrelationship would clearly be important for breast cancer etiology, early detection and prevention. In the presentstudy associations between EBV, MMTV and Merkel cell polyoma virus and breast cancer in 100 Iranian patientswere evaluated using paraffin-embedded tissues. EBER RNA and expression of p53 and large T antigen wereevaluated by real time PCR and CD34, p63, HER2, PR and ER markers were studied by immunohistochemistry.EBV was detected in 8/100 (8%), MMTV in 12/100 (12%), MPy in 3/100 (3%) and EBER RNA in 18/100 (18%)cases. None of the control samples demonstrated any of the viruses. p53 was suppressed in EBV, MPy and MMTVpositive samples. The large T antigen rate was raised in MPy positive samples. Our results showed that EBV,MMTV and the Merkel cell polyoma virus are foundwith some proportion of breast cancers in our patients,suggesting that these viruses might have a significant role in breast cancer in Kerman, southeast of Iran .