Objective:To investigate the expression of Let-7c in patients with invasive ductal carcinoma of the breast cancer and its correlation with the clinicopathologic features of the patients. Methods: The expression of Let-7c was examined in 40 tissues of invasive ductal carcinoma of the breast cancer and their matched non-tumor adjacent tissue specimens by stem-loop real-time RT-PCR. The correlation of the expression with the clinicopathological features of breast cancer, such as the clinical staging, lymphatic metastasis, and proliferation index, was analyzed. Results: The stem-loop realtime RT-PCR was sensitive and specific in detecting Let-7c expression. Expression of Let-7c in breast cancer tissues was significantly lower than that in the adjacent normal tissues(P＜0.05). Down-regulation of Let-7c expression was associated with higher proliferation index (Ki-67＞10%) (P=0.030) and the status of Estrogen/Progesterone receptor (P=0.040/0.034)in breast cancer patients. There was no significant association of Let-7c expression with menopause condition, breast cancer TNM clinical stage, or lymphatic metastasis(P＞0.05). Conclusion: Our results suggest Let-7c may play an important role in the development of breast cancer and the level of Let-7c expression may be a potential parameter in forecasting the progression and prognosis of breast cancer patients.