Abstract： As an increasing threat of women's health worldwide, breast cancer has many well-established risk factors, including early-age menarche, late-age menopause,post menopausal obesity,improper use of hormone therapy and genetic susceptibility. However, these risk factors only account for about half of the incidence and mortality of breast cancer. Recent studies provide many clues that three primary hormone responsive virus: Epstein-Barr virus(EBV), human papilloma viruses (HPV) and mouse mammary tumor virus (MMTV) may act as important agents of human breast cancer.