Objective To explore the possible mechanism of Modified Simiao Decoction（加味四妙方） on hyperuricemia（HUA） and acute gouty arthritis（GA）. Methods A total of 48 male Wistar rats were randomly divided into a control group

a model group

a Modified Simiao Decoction low dose group

medium dose group

high dose group

and a western medicine group with 8 rats in each group. The low

medium

high dose group of Modified Simiao Decoction were respectively given 16.8、33.6、67.2 g/（kg·d）by gavage

and the western medicine group was given 0.09 g/kg allopurinol plus colchicine 0.05 mg/100 g. The control group and model group were given intragastric administration with 10 ml/kg distilled water. All groups were continuously administered for 7 days. Except for the control group

rats were injected intraperitoneally with 3% potassium oxazidate solution to establish the HUA model

and then the sodium urate solution was injected into the right ankle joint cavity of rats to induce the GA model. The changes of rat ankle joint diameter

the levels of blood uric acid（SUA） and C-reactive protein（CRP）

and the nucleotide binding oligomerization domain-like receptor protein 3（NLRP3） mRNA of ankle joint tissue were detected. Interleukin 1β（IL-1β） and tumor necrosis factor α（TNF-α） expression were observed. Results Compared with the control group

ankle circumference

level of serum SUA and CRP

and expression of NLRP3 mRNA

IL-1β and TNF-α in ankle tissue were significantly increased in the model group（P<0.01）. Compared with the model group

the ankle joints circumference

serum SUA and CRP levels

expression of NLRP3 mRNA

IL-1β

and TNF-α in the ankle tissue were significantly decreased in the medium and high dose group of Modified Simiao Decoction

and the western medicine group（P<0.05）. Compared with Modified Simiao Decoction high dose group

the serum CRP level and the expression of NLRP3 mRNA in ankle joint tissue in the western medicine group were significantly reduced（P<0.05）. Conclusion Modified Simiao Decoction can relieve joint swelling of HUA combined with GA and reduce level of SUA. Its mechanism may be related to the regulation of the secretion of NLRP3 inflammasome and downstream inflammatory factors IL-1β and TNF-α.