Abstract： Objective To discuss the effect of continuous blood purification (CBP),thymosin α1 and combined therapy on cellular immunity in patients with severe sepsis. Methods Ninety-one patients,age over 18 years,suffering from severe sepsis with Marshall score over 5,admitted to the intensive care unit (ICU) from June,2004 to October,2007,were randomly divided into four groups. The patients in control group (24 cases) were treated with classical Surviving Sepsis Campaign (SSC) therapy,those in CBP group (22 cases) were treated with continuous renal replacement therapy (CRRT) or molecular adsorbent recirculating system (MARS) in the first 3 days. The group of thymosin α1 (23 cases) were treated with thymosin α1,in a dose of 1.6 mg subcutaneous injection per day for 7 days. The patients in the group of combined therapy (22 caese) were treated with CBP and thymosin α1. All three treatment groups were treated with classical SSC therapy at the same time. Acute physiology and chronic health evaluationⅡ (APACHEⅡ) score and Marshall score were evaluated. CD14+ monocyte human leucocyte antigen DR (HLA-DR) levels and the count of T lymphocyte were measured before treatment and 3 days and 7 days after the treatment. Results All 91 patients were included in the study. Compared with the control group,the 28-day mechanical ventilation (MV) time,length of ICU stay,28-day mortality of three treatment groups were decreased. There was statistically significant difference in the length of ICU stay of the CBP group,and also the 28-day MV time,length of ICU stay of the group of combined therapy group (all P<0.05). Compared with the variables before treatment,Marshall scores were decreased significantly and levels of HLA-DR,CD3+,CD4+,CD8+ T lymphocytes were increased significantly after 7-day treatment with thymosin α1 group (all P<0.05). The above indexes and APACHEⅡ scores were changed significantly as early as 3 days after treatment in CBP group and combined therapy group (P<0.05 or P<0.01). Compared with the variables at the same period in the control group,only CD3+ T lymphocytes were increased significantly after 7-day treatment in thymosin α1 group (P<0.05),APACHEⅡ scores and Marshall scores were decreased significantly,leves of HLA-DR and CD3+,CD4+,CD8+ T lymphocytes were increased significantly after 7-day treatment in CBP group (all P<0.05). The above indexes were already changed significantly after 3-day treatment in the combined therapy group (P<0.05 or P<0.01). Compared with thymosin α1 group,all the indexes were improved but only level of CD3+ T lymphocytes after 3-day treatment in the combined therapy group increased significantly (P<0.05). Conclusion CBP and thymosin α1 could increase cellular immunity in patients with severe sepsis,promote recovery of organ function and improve prognosis. The effect of CBP appears earlier and more pronounced. Combined treatment can be more effective.