Objective:To observe the therapeutic effect of arsenious acid combined with Tα-1 thymuspeptide and megestrol acetate on advanced non-small cell lung cancer. Methods: Nintey-two patients weredivided randomly into the treated group(n= 45) and the control group(n= 47). The treated group weretreated with arsenious acid combined with Tα-1 thymus peptide and megestrol acetate, and the controlgroup were treated with chemotherapy in the NP protocol. Results: (1) Therapeutic effect: In the 36 pa-tients of the treated group, 2 were evaluated as CR, 8 as PR, 9 as MR, 8 as SD and 9 as PD, the CR+PRrate being 27.7% (10/36), while in the 40 patients of the control group, the corresponding numbers were3, 10, 11, 9, 7 and 32.5% (13/40). Comparison between the CR+PR rate between the two groupsshowed insignificant difference (P＞0.05). (2)Clinical benefit rate: The positive rate of Karnofsky scoresin the treated group and the control group was 44.4 % and 20.0 % respectively; and the positive rate ofbody weight in the two groups was 33.3 % and 12.5 % respectively, the difference between the two groupswas significant ( all P＜0.05). (3)Changes of T- cell subsets and NK cell activity: CD4 and CD4/CD8 ra-tio after treatment in the treated group increased significantly (P＜0.05), while in the control group,CD3, CD4, CD4/CD8 ratio and NK cell activity all lowered significantly (P＜0.01). Comparison betweenthe two groups after treatment showed significant difference in CD4, CD4/CD8 ratio and NK cell activity,with those in the treated group all higher than those in the control group (P＜0.01). (4)Adeverse-reac-tion: No serious adverse reaction was found in both two groups. (5)Median survival period: The treatedgroup was 30 weeks and that in the control group was 28.5 weeks, and the difference between the twogroups was insignificant (P＞0.05). Conclusion: Arsenious acid combined with Tα-1 thymus peptide andmegestrol acetate was a relatively effective scheme with low toxicity in treating advanced NSCLC.