Objective To investigate the expression of carnitine palmitoyl transferase 1 (CPT1) in breast cancer and study its role in the pathogenesis and development of breast cancer. Methods CPT1 expression in 211 cases of human breast cancer tissues and non- cancerous adjacent breast tissues was examined by immunohistochemistry. The relationship between the differential expression of CPT1 and the clinicopathological variables was analyzed as well. Results The expression rate of CPT1 was 66.35% in breast cancer tissues and 6.16% in non- cancerous adjacent breast tissues(P 0.05), menopausal status(P> 0.05),and progesterone receptor (PR)status(P> 0.05). Conclusion CPT1, up- regulated in the breast cancer tissue, could meet the high energy need of proliferation,invasion and metastasis, and is correlated with the pathogenesis and development of breast cancer. Key words: Breast cancer; Carnitine palmitoyl transferase 1; Fatty acid beta- oxidation; Proliferation