Objective To investigate the effect of thymosin α1 on immunity,metabolism and prognosis in elderly patients with sepsis followed by persistent inflammation,immunosuppression,and catabolism syndrome (PICS).Methods In this retrospective study,68 patients diagnosed with sepsis followed by PICS in medical intensive care unit (MICU) from Jan.2014 to Dec.2016 were involved.Thirty-four patients treated with thymosin α1 for 2 weeks were allotted to the observational group;other 34 patients were to the control group.Patients' clinical information and data of laboratory test were collected in addition.We compared patients' general information,and the indexes before and after treatment,then the indexes between the two groups to analyze the effect of thymosin α 1 on immunity and metabolism;moreover,we conducted survival analysis and compared the mortality of different periods to analyze the effect of thymosin α1 on prognosis.Results The number of monocytes,the levels of CD4/CD8 and HLADR/CD14 before and after treatment in the observational group were significantly higher than those in the control group [(0.11 ± 0.31)× 109/L vs.(-0.16 ± 0.36)× 109/L,(0.20 ± 0.94) vs.(-0.22 ± 0.74) and (5.8 ±16.3)％ vs.(-3.3 ± 18.2)％ respectively],which suggested that the number of monocytes and the levels of CD4/CD8 and HLADR/CD14 were significantly increased by thymosin α1 intervention,and the difference were statistically significant(P ＜ 0.05).Kaplan-meier survival analysis showed prognosis between the two groups was not statistically significant (P ＞ 0.05).The further analysis of mortality in different periods indicated that the mortality within 28 days,90 days and 120 days and overall mortality between the two groups [8 (23.5％) vs.12 (35.3％),18(52.9％) vs.25 (73.5％),20 (58.8％) vs.27 (79.4％) and 24 (70.6％) vs.28 (82.4％) respectively],were not statistically significant(P ＞ 0.05).Conclusions Thymosin α1 can be used to regulate the immunity of elderly patients with sepsis followed by PICS,but its effect on regulating metabolism and improving prognosis needs further study.