This paper reports the effects of Tripterygium Wilfordii (TW) on adrenal cortex in rats with adjuvant arthritis. Forty rats were divided into 5 groups. Adjuvant arthritis (AA) models were made with complete freund's adjuvant (CFA) in groups I-IV. Each of which was treated with sodium carboxyl methyl cellulose, TW, prednisone and cyclophosphamide respectively. The untreated rats allocated to group V served as normal controls. The swelling of AA markedly subsided in group II, III and IV as compared with group I (P < 0.01), whereas no significant differences were noted among groups II, III and IV (P > 0.05). The obviously increased plasma corticosterone levels and decreased adrenal ascorbic acid levels were observed in group II, whereas decreased plasma corticosterone levels and increased adrenal ascorbic acid levels were noted in group III. There was a striking contrast between groups II and III. The morphological changes of adrenal glands under light microscope revealed hypertrophic adrenal cortices in group II, and atrophic adrenal cortices in group III. The above findings suggest that the effect of promoting production of corticosteroids may be one of the mechanism by which TW can effectively treating autoimmune diseases.