Abstract: Objective To evaluate effects of radiation therapy based on pemetrexed combination with cisplatin or carboplatin regimen on the peripheral lymphocyte subsets in patients with non-small cell lung cancer(NSCLC). Methods A total of forty-five patients with a pathologic diagnosis enrolled in this study were treated with pemetrexed 500 mg/m2 infusion on day 1 and cisplatin 25 mg/m2 infusion on day 1 to 3 or carboplatin area under the curve(AUC)5 infusion on day 2.The peripheral blood was collected before and five days after chemotherapy.Every patient must be evaluated with the flow cytometry for CD3+,CD4+,CD8+,CD4+/CD8+,CD16+56+ and CD19+. Results The expressive rates of CD4+,CD16+56+ and CD4+/CD8+ in peripheral blood in post-treatment patients were higher than that in pre-treatment samples (P=0.032).No evident case of changes of CD3+,CD8+,and CD19+ positive cell percentage were observed after chemotherapy(P>0.05).Before chemotherapy,the positive percentage of CD3+,CD4+,CD16+56+ and the ratio of CD4+/CD8+ in NSCLC ⅢB～Ⅳ clinical stage were statistically significantly lower than those in ⅠB～ⅢA clinical stage patients（P=0.029）,but were not different from those after chemotherapy(P>0.05).CD3+,CD4+ and the ratio of CD4+/CD8+ in the effective group were highter than those in pre-treatment samples（P=0.008）. Conclusion The immune function of advanced stage NSCLC patients is evidently suppressed.Pemetrexed combination with cisplatin or carboplatin regimen for NSCLC may break up anti-tumor immune suppression,then a transient immune suppression condition is reversed by the body rebuilding to enhance the immune function.