Objective To investigate the relationship between blood CD4 + CD25 + regulatory T cells ( Treg cells) and cell immunity in patients with sepsis and its prognostic value.Methods 27 patients with sepsis admitted during August 2007 and August 2008 in ICU were enrolled, while 40 healthy volunteers served as control. According to the clinical outcome after 28 days’ treatment, the sepsis patients were assigned to a death group( n=8) and a survival group ( n =19) . Blood Treg% and CD4 /CD8 were detected by flow cytometry and total AgNOR area/nucleus area per cell ( IS%) was measured by silver nitrate staining and image processing. Results The Treg% in the patients with sepsis was significant higher than that in the normal control [ ( 5. 61 ±1. 60) % vs. ( 0. 78 ±0. 23) % , P lt; 0. 01 ] , while the level of CD4 /CD8 and IS% were significant lower[ CD4 /CD8: ( 1. 09 ±0. 30) vs. ( 1. 71 ±0. 36) , IS% : ( 5. 19 ±1. 07) % vs. ( 6. 76 ±0. 92) % , both P lt; 0. 01] . Significant correlations were found between Treg% and CD4 /CD8( r= - 0. 484, P lt;0. 01) , and between Treg% and IS% ( r = - 0. 588, P lt;0. 01) . Compared with the survival group, Treg% was significant higher [ ( 7. 09 ±1. 17) % vs. ( 5. 00 ±1. 33) % , P lt; 0. 01] , and CD4 /CD8 and IS% were significant lower[ CD4 /CD8: ( 0. 87 ±0. 22) vs. ( 1. 18 ±0. 29) , IS% : ( 3. 97 ±0. 42) % vs. ( 5. 71 ±0. 81) % , both P lt; 0. 01] in the death group. Conlusion Blood Treg% level can reflect the cell immune state of patients with sepsis and is of clinical value to assess the prognosis.