The aim of this study is to investigate the expression of mTOR in breast cancer and observe the effect of CCI-779 on proliferation and apoptosis of MDA-MB-231 cells. Immunohistochemical staining was used to detect the expression of mTOR protein in breast cancer tissues and MDA-MB-231 cells. MTT assay was used to assess the effect of CCI-779 on proliferation of MDA-MB-231 cells. Annex-inV-FITC/ PI assay was utilized to evaluate the effect of CCI-779 on apoptosis of MDA-MB-231 cells. Among the 71 cases of breast cancer tissues, 54.9% were mTOR-positive that exhibited significantly higher expression than the 32 cases of normal tissues (21.9%); mTOR protein was also found to be expressed in MDA-MB-231 cells. The mTOR inhibitor CCI-779 significantly inhibited the proliferation of MDA-MB-231 cells that was dose- and time-dependent. However, CCI-779 was unable to induce apoptosis of MDA-MB-231 cells as demonstrated with AnnexinV-FITC/PI assay. mTOR plays a key role in the initiation and development of breast cancer, and its inhibitor CCI-779 exerts a strong suppressive activity against MDA-MB-231 cells, suggesting its therapeutic potential to treat breast cancer.