Objective To investigate the effects of ulinastatin on Treg/Th17 and immune status in patients with severe sepsis.Methods A total of 80 patients with severe sepsis, who were hospitalized in ICU during October 2011 to July 2012, were randomly divided into a routine group and a ulinastatin group. The patients in the ulinastatin group were intravenously administered 30mg ulinastatin three times per day for 5 days in addition to routine bundle treatment. The expression of Treg, Th17 and HLA-DR were detected on the first day in ICU and 5 days after treatment. 20 healthy individuals served as controls. Results Compared with the control group, the severe sepsis group had overexpression of Treg and Th17 ( P lt;0. 01) , higher ratio of Treg/Th17( P lt;0. 01) , and decreased HLA-DR expression of CD14 monocyte ( P lt; 0. 01) . In the severe sepsis patients, ulinastatin injection reduced the abnormal expression of Treg and Th17 ( P lt; 0. 01) , decreased the ratio of Treg/Th17( P lt; 0. 01) , and improved the expression of HLA-DR ( P lt; 0. 01) more effectively compared with the routine treatment. Ulinastatin also lowered 28-day mortality of the patients with sepsis, but the difference between the ulinastatin group and the routine group was not significant. Conclusions In severe sepsis patients, there were abnormal overexpression of Treg and Th17, imbalance of Treg/Th17, and underexpression of HLA-DR which imply an immune suppression. Ulinastatin can decrease the expression of Treg and Th17, inverses the ratio of Treg/Th17, and improve the expression of HLA-DR, so as to improve the prognosis of severe sepsis patients.