Abstract: OBJECTIVE To investigate the effect and mechanism of Valeriana jatamansi Jones. extract Jatamanvaltrate P on proliferation of T47D cells to breast cancer. METHODS MTT assay was used to detect the effect of Jatamanvaltrate P on T47D and BT-20 cells; DAPI staining and flow cytometry(FCM) were used to examine cell cycle and apoptosis; Western blot assay was performed to detect the expression of related proteins of cell cycle and apoptosis. RESULTS Jatamanvaltrate P significantly inhibited the breast cancer cells in a time-and dose-dependent; Jatamanvaltrate P induced cell cycle arrest at G₂/M phase, and the expression of cycle associated proteins Cyclin B1 and cdc2 was decreased, while p-cdc2 was increased; Jatamanvaltrate P was able to induce T47D cells to produce apoptotic bodies and significantly increase the apoptosis rate of T47D cells in a dose-dependent manner. The proteins of PARP, Caspase 3, Caspase 8 and Caspase 9 produced activated form in T47D cells by treatment with Jatamanvaltrate P. CONCLUSION Jatamanvaltrate P may be possible to inhibit the proliferation of T47D cells by cell cycle arrest and inducing apoptosis, which is expected to become a potential drug for the treatment of breast cancer.