Abstract: Objective: To study the expression of P-glycoprotein (P-gp) in human non-cancerous lung tissue and the correlation between the expression of P-glycoprotein in the primary lesion and in the metastatic lymph node of patients with lung cancer． Methods: 40patients with regional lymph node metastasized lung cancer of previously untreated and 10non-cancerous lung tissues were studied for the expression of P-glycoprotein by means of immunohistochemistry．Results: In 40 patients with lung cancer，23patients had positive expression in primary lesion，among these 23 patients，18patients showed positive expression in metastatic lymph node and the other 5patients show negative expression of P-glycoprotein (P-gp) in primary lesion，among the other 17 patients who showed negative expression of P-glycoprotein in primary lesion，no one showed positive expression in metastatic lymph node．In 10 patients with normal lung tissue showed negative expression of P-glycoprotein．There was a correlation between the expression of P-glycoprotein in the primary lesion and in the metastatic lymph node of patients with lung cancer, but no difference between the expression of P-glycoprotein and histologic subtypes with lung cancer．Conclusion: In the patients with lung cancer，the expression of P-glycoprotein in the metastatic lymph node correlated with the expression in the primary lesion．The expression of P-glycoprotein(P-gp) in human non-cancerous lung tissue showed negative．