Abstract: HT5"HAbstract:HT5"SSSince the mouse mammary tumor virus (MMTV) was discovered for the first time to be associated with the human breast cancer, researchers have persevered with study of the hypothesis of MMTV as a human pathogen associated with breast cancer. The main aspects of these studies included the gene level, immunological response and epidemiology. Many studies supported the view that there was relationship between the MMTV and the human breast cancer, in particular, there were many aspects of gene level evidence, for example, the finding of MMTV integration sites into DNA of human breast cancer cells, the presence of sequences resembling MMTV in patients with breast cancer, and so on. Unfortunately, strong convincing direct evidence remained absent. In addition, some of results were just the opposite. Therefore, continuous research is necessary in order to provide more substantial evidence to verify the presence or absence of MMTV, and its potential role in breast cancer.