AIM: To explore the mechanism of decreased cellular immune function and the effect of Jinhong Tablets, a Chinese herbal medicine, during the course of obstructive cholangitis. METHODS: An obstructive cholangitis model was induced in 24 male Sprague-Dawley rats that were randomly divided into model (n=8), Jinhong Tablet-treated (n=8) and simple obstructive cholangitis (n=8)groups. Four days after modeling, all rats were sacrificed and the interleukin (IL)-2, CD3+, CD4+ and CD8+ levels in plasma were measured by enzyme liked immunosorbent assay (ELISA). The endotoxin content was detected by a reagent kit. The index of apoptosis was determ ined by Tdt-mediated flu-orescein-dUTP nick end labeling (TUNEL), and ultrastructure changes of the thymus and apoptosis were observed by electron microscopy. RESULTS: Plasma IL-2, CD3+, and CD4+ levels and the thymus mass index in the untreated group were significantly lower than those in the Jinhong Tablet-treated and simple ligation groups (IL-2: 28.5±3.0 ng/L vs 33. 9土3.6 ng/L, 39.6±2.2ng/L, P<0.05, P<0.01; CD3:54.5%±5.5% vs 70.7%±4.8%, 66.3%±7.1%, both P<0.01; CD4: 34.5% 土8.3% vs 44.2% ±3.3%, 4.5% ±4.2%, both P<0.01; thymus index: 0.89±0.18 vs 1.10±0.13, 1.12±0.24, both P<0.05). There were no significant differences among the three groups with regard to the level of plasma CDR, while plasm a endotoxin and the thymus apoptosis index in the untreated group were significantly higher than in the Jinhong Tablet-treated and simple ligation groups rendotoxin: 0.85±0.14 EU/ml vs 0.53±0.10 EU/mL, 0.49±0.11 EU/ml, both P<0.01; thymus index: 25.7±5.1 vs 15.8土5.5, 9.0±3.1, P<0. 05, P<0. 01). More typical apoptosis cells were seen in thymus tissue than in the untreated group. The results demonstrated that intervention by traditional Chinese medicine improved the immune function, endotoxemia and thymus cell apoptosis, even approaching the levels in the simple obstructive cholangitis. CONCLUSlON: Decreased cellular immune function and abnorm al apoptosis of thymus cells exists in rats with obstructive cholangitis; Jinhong Tablets sign ificantly improve the regulation and maintenance of immune function.