Objective To study the effects of high fat diet on joints of collagen-induced arthritis rats by comparing different diets. Methods After the model of Wistar CIA rats was established, We feed normal and high fat diet. The arthritis index scores were measured and the synovium were examined with HE stain and the concentrations of lipids and inflammatory factors in serum were detected. Results Compared with those in normal group, the arthritis index scores, synovial proliferation, pannus formation and inflammatory cell infiltration in synovium HE stain were increased in CIA rats with high fat diet. Plasma levels of TC and LDL were also enhanced in high fat diet CIA rats group(P<0.05) apart from HDL, which were decreased obviously(P<0.05).Plasma levels of Pro-inflammatory cytokines,that is TNF-α, IL-1β and IL-17 were also significantly increased in high fat diet CIA rats. Conclusions High fat diet may promote the progress of arthritis in CIA rats by enhancing synovial hyperplasia and inflammatory cytokines.