Abstract: Objective To explore the efficacy of thymosin combined with chemotherapy in treatment of patients with non-small cell lung cancer (NSCLC) and its influence on immune function.Methods A total of 200 patients with NSCLC were selected and randomly divided into observation group and control group.All patients were treated with combined treatment,including vinorelbine plus cisplatin (NP),paclitaxel plus cisplatin (DP) and gemcitabine plus cisplatin (GP).On this basis,patients in observation group were treated with thymosin.Changes of T lymphocyte subsets and NK cells were compared before treatment and 7,28 days after chemotherapy between two groups,and the toxic reactions such as bone marrow depression and gastrointestinal reaction were observed.Results Seven and twenty-eight days after chemotherapy,there were significant differences of T lymphocyte subsets and NK cells between two groups (P ＜ 0.05).The incidence rate of myelosuppression in the observation group was 29％,which was significantly lower than 53％ in the control group (P ＜ 0.05).The incidence rate of gastrointestinal reaction in the observation group was 63％,which was significantly lower than 98％ in the control group (P ＜ O.05).Conclusion Chemotherapy combined with thymosin can significantly improve immunity ability of patients with non-small cell lung cancer,and reduce the toxicity of anti-cancer drugs.