Objective To explore the relationship between the loss of the heterozygosity of nm23-H_1 and the lymph node metastasis in no-small-cell lung cancer (NSCLC). Methods The loss of the heterozygosity of nm23-H_1 gene of cancer tissue and peri-cancerous tissue was detected in 39 patients with NSCLC by Southern blotting. Results The heterozygosity gene of nm23-H_1 is 7.6 kb and 2.3 kb. The LOH rate of the patients with lymph node metastasis (48%, 12/25) was higher than those without lymph node involvement (8%, 1/11) (P