Abstract: Objective: To study the inhibitory action and induced apoptotic effect of Paclitaxelnanometer (NP) on BCML-TA299-bearing mice in vivo. Methods: The inhibitory effect on tumors was observed in BCML-TA29-bearing mice. The expression of bax mRNA was assessed by in situ hybridization and flow cytometry. Growth inhibition was assessed and microscopy was also utilized. The data were used to examine the effect of Paclitaxel-NP on BCML-TA299 breast cancer. Results: The growth of BCML-TA299 was markedly inhibited by Paclitaxel-NP in vivo in a concentration-dependent manner. The expression of proapoptotic Bax was increased. Conclusion: Paclitaxel-NP may significantly inhibit the growth of breast cancer in mice by inducing apoptosis and inhibiting proliferation of the tumor cells.