Abstract: Objective : To explore the clinical significance and sensitive of molecular diagnosis of detecting micromatastasis in lymph node from non-small cell lung cancer patients Methods : The MUC1 mRNA expression was detected in 119 lymph nodes from 31 lung cancer patients and 35 lymph nodes from 10 benign pulmonary lesion patients by nested RT-PCR. Results : The sensitive of RT-PCR technique was 10^-6 in this study. In the 119 lymph nodes from lung cancer patients, MUC1 mRNA expression (54.5%, 65/119) was detected in 65 lymph nodes by RT-PCR. Cancer metastasis (34.5%, 41/119) was observed in 41 lymph modes by HE staining. None of MUC1 mRNA expression was observed in all the 35 lymph nodes in the benign pulmonary lesion groups. The micromatastasis in lymph nodes were closely related to the pathological classification, cell differentiation of the cancer and P-TNM stage of the disease (P<0.05). Conclusion : RT-PCR technique is a specific and sensitive method to detect micromatastasis in patients with lung cancer. MUC1 mRNA might be a valuable marker to detect micromatastasis in lung cancer patients. It can also provide important clinical information for the evaluation of prognosis and in the selection of appropriate treatment strategies.