Abstract： Background Cryptotanshinone (CT) was originally isolated from the dried roots of Salvia militorrhiza, an herb that is used extensively in Asian medicine and the extracts of this herb have been used in the treatment of several pathologies, including cardiovascular diseases, hematological abnormalities, hepatitis, and hyperlipidemia, but no studies had been carried on the treatment for rheumatic diseases with it.This study aimed to investigate the effects of cryptotanshinone on immune functions in rats with adjuvant arthritis (AA).Methods Complete Freund's adjuvant was used to induce AA in rats. Thymus and spleen was aseptically taken from normal rats and the AA rats. Then a thymus lymphoid cell suspension, splenic lymphoid cell suspension and peritoneal macrophage cell suspension were prepared. After adding CT (0.1 μg/ml, 1.0 μg/ml, 10 μg/ml, 100 μg/ml, 1000 μg/ml) into the suspension, T and B lymphocytes proliferation was determined by 3-(4,5-2 dimethylthiazal-2yl)2,5-diphenyltetrazoliumbromide (MTT) assay. And the activities of interleukin-1 (IL-1) and IL-2 were measured by the mouse lymphocytes proliferation assay.Results Thymic T and splenic B lymphocyte proliferation of the AA rat was significantly lower, and could be stored through using CT in vitro. CT (100 μg/ml and 1000 μg/ml) increased T or B lymphocytes proliferation in vitro (P <0.01). In AA rats, the levels of IL-1 released by abdominal PMΦ significantly increased whereas the level of IL-2 released by T cells decreased in vitro. CT (1000 μg/ml) decreased the production of IL-1 and promoted production of IL-2 in vitro (P<0.05). Conclusions CT can ameliorate the abnormal immunological functions in AA rats.