Objective: To observe the variation of T-cell subsets in spleen in different course of disease and tissue histopathological changes in rats with adjuvant arthritis (AA).Methods: The model of rat AA was induced by complete Freunds adjuvant into the right hind metatarsal footpad of 20 male Lewis rats.Arthritis was evaluated by total score, arthritis index and paws swelling number.The percentage of total (CD3+CD4+), memory (CD4+CD44+), no-sensitizated (CD4+CD62L+) and Th1 7 (CD4 IL-17+) on CD4+T cells in spleen were detected by flow cytometry at days 14 and 22 after immuniozation.The histopathological evaluation of heart, liver, spleen, lung, kidney, ankle joims and mesenteric lymph nodeswere examined by hematoxylin and eosin (HE) stain.Results: The onset of secondary arthritis appeared on about day 10 after immunization, with a peak onset on day 19.Systematic arthritis symptoms included front and hind paw swelling and redness (swelling was more apparent in the front rather than hind paws),nodule formation and redness on the ears, connective tissue swelling and redness of the nose and evident nodules and redness on the tail.Total score, arthritis index and the paws swelling numbers were enhanced in AA rats.Pathohistology of ankles joints showed hyperplasia, pannus formation, and inflammatory cells infiltration in AA rats.And pathohistology of heart, liver, spleen, kidney and mesenteric lymph nodes showed inflammatory changes.Compared with normal group, there is no change of the percentage of total, memory and no-sensitizated CD4+T cell in the early stage inflammation but significantly enhanced in the peak of inflammation.Th17 cell subsets were significantly enhanced in both of the early and peak of inflammation.Conclusions: These findings suggest that abnormal T cell responses and tissue histopathological changes are important features of AA rats.