OBJECTIVE： To observe clinical efficacy and safety of thymosin in adjunctive treatment of chronic eczema， and to investigate its mechanism from the change of peripheral T lymphocyte subsets. METHODS： 160 patients with chronic eczema were randomly divided into observation group and control group， with 80 cases in each group. Both group received conventional therapy as mizolastine， Desonide cream. Observation group additionally received Thymosin enteric-coated tablet 20 mg，po， tid； control group was given placebo the appearance of which was same with Thymosin enteric-coated tablet. Treatment course lasted for 4 weeks. The change of T lymphocyte subsets， clinical efficacy and the occurrence of ADR were compared between 2 groups. Recurrence rate of both groups were followed up for 1 year. RESULTS： The effective rate of observation group （91.25％） was significantly higher than that of control group（77.50％）， with statistical significance（P＜0.05）. After treatment， CD4+ and CD4+/ CD8+ of 2 groups were significantly increased， while CD8+ was decreased significantly； CD4+ and CD4+/ CD8+ of observation group were significantly higher than those of control group， with statistical significance （P＜0.05）， but there was no statistical significance in CD8+ between 2 groups （P＞0.05）. There was no statistical significance in the incidence of ADR between 2 groups （P＞0.05）. Recurrence rate of observation group （31.51％） was significantly lower than that of control group （64.52％） during follow-up period， with statistical significance（P＜0.05）. CONCLUSIONS：  In summary， thymosin can improve clinical efficacy and reduce recurrence rate by regulating T lymphocyte subsets with good safety.