Previous studies have demonstrated that the total alkaloids of Sophora alopecuroides (TASA), which contains many different ingredients like sophocarpine, matrine, oxymatrine, sophoridine, sophoramine, aloperine and cytosine, were able to protect colon against ulcers caused by 2,4,6-trinitrobenze sulphonic acid (TNBS)/ethanol treated models. In order to elucidate the mechanisms by which TASA exerts its effect of anti-inflammation and immunoregulation on rats with colitis, DAI (disease activity index) and histological grading of colitis were evaluated in the animal model. Moreover, the expression of CD4(+)CD25(+) regulatory T cells (Tregs) and IL-10 in rats with experimental colitis were observed by FCM, ELISA and RT-PCR in this study. Results showed that TASA (15, 30 or 60 mg/kg/day) significantly up-regulated CD4(+)CD25(+)Tregs (P = 0.02, P = 0.02, P = 0.03) and IL-10 levels (ELISA: P = 0.03, P = 0.02, P = 0.00; RT-PCR: P = 0.04, P = 0.02, P = 0.01) respectively and decreased the DAI and histological grading of colitis in the peripheral blood (PB) and colon of rat colitis models (3.44 +/- 1.53, 4.25 +/- 1.27, 4.42 +/- 1.24 and 3.50 +/- 1.42, 4.05 +/- 1.32, 4.51 +/- 1.55 vs. 7.18 +/- 1.32 and 7.38 +/- 1.52, P < 0.05, P < 0.01, respectively). Most interestingly, a negative correlation was demonstrated between the expression of CD4(+)CD25(+) Tregs and DAI (Pearson r(PB) = -0.677, P < 0.01; Pearson r(COLON) = -0.663, P < 0.01, n = 60), or histological grading of colitis (Pearson r(PB) = -0.725, P < 0.01; Pearson r(COLON) = -0.623, P < 0.01, n = 60). Simultaneously, a positive correlation existed between CD4(+)CD25(+) Tregs and IL-10 cytokine (IL-10 mRNA) in the colon and PB of rats (Pearson r(PB) = 0.789, P < 0.01, n = 60; Pearson r(COLON) = 0.678, P < 0.01, n = 60). These results may explain to some extent the mechanisms of TASA on treating rats with experimental colitis.