The effect of dihydromyricetin (DMY) on recurrent oral ulcer (ROU) in rabbits was studied. The ROU model was established by injection of immunogen composed of the homogenate supernate of homogeneous oral oral mucosa from New Zealand rabbits and Freund's complete adjuvant (FCA) into rabbit backs at multi-points of 2 sides of backbones s.c. once every 2 wk for 5 times. Seven days after the 5th immunogen injection, DMY was given to the surface of oral mucosa for 4 d. The day after the last administration, oral mucosa was collected for pathol. The blood serum and plasma were collected for malondialdehyde (MDA) contents and SOD activity detection, TXB2 and 6K-PGF1α detection, resp. Lymphocyte was separated for CD4+ and CD8+ masculine cell population detection. Rabbit ROU models had the pathol. change of inflammation, necrosis, ulcer, etc. in the mucosa. SOD activity in the serum, 6K-PGF1α and CD4+ in the plasma decreased while MDA in the serum, thromboxane B2 (TXB2) and CD8+ in the plasma rose. The pathol. changes of the mucosa ulcer lessened obviously after the DMY administration. SOD activity increased while the production of MDA and TXB2 (T) decreased. The content of 6K-PGF1α increased and led to T/P ratio. Masculine cell population of CD4+ increased and CD8+ decreased, resulting in increased ratio of CD4+/CD8+. The effect of DMY on ROU in rabbits could be through regulating the activity of T lymphocyte subpopulation, the level of vasomotion materials and its antioxygen damage role.