Objective To research the analgesic effect and possible mechanism of Shexiang Wulong Pills for rheumatoid arthritis（ RA）. Methods Sixty Wistar rats were randomized into the normal group

model group and lowdose

middle-dose and high-dose Shexiang Wulong Pills groups

with 12 in each. All rats were injected with complete Freund’s adjuvant for modeling except rats in the normal group. From the 15 th day of modeling

the low-dose

middledose and high-dose Shexiang Wulong Pills groups were gavaged with 0. 3

0. 6 and 1. 2 g /（ kg·d） Shexiang Wulong Pills once daily for 2 weeks. The normal group and model group were gavaged with equal volume of normal saline once daily for 2 weeks. The rats were sacrificed 2 weeks later. The tissue morphology of pituitary was observed under light microscope after HE staining. The expressions of adrenocorticotropic hormone（ ACTH） and β-endorphin（ β-EP） in the pituitary were detected with immunohistochemistry. Results The tissue morphology of pituitary was not significantly changed. Comparing with the normal group

the expressions of ACTH and β-EP were significantly increased in the model group and low-dose

middle-dose and high-dose Shexiang Wulong Pills groups（ P < 0. 01）. Comparing with the model group and low-dose Shexiang Wulong Pills group

the ACTH expression was significantly decreased in the middledose and high-dose Shexiang Wulong Pills groups（ P < 0. 05 or P < 0. 01）. Comparing with the model group

the β-EP expression was significantly increased in the low-dose

middle-dose and high-dose Shexiang Wulong Pills groups（ P <0. 01）. Comparing with the low-dose Shexiang Wulong Pills group

the β-EP expression was significantly increased in the middle-dose and high-dose Shexiang Wulong Pills groups（ P < 0. 05 or P < 0. 01）. Conclusion Shexiang Wulong Pills can regulate the expressions of ACTH and β-EP in the pituitary of RA rats

which may be one of the mechanisms of analgesia.