OBJECTIVE: To evaluate the effect of Tanreqing injection on axon myelin in the mouse brain of experimental autoimmune encephalomyelitis (EAE). METHODS: An EAE model was established by myelin oligodendrocyte glycoprotein (MOG)(35-55) immunization in C57BL/6 mice. Mice were randomly divided into the following groups: normal, model, prednisone acetate (PA) (6 mg/kg), Tanreqing high dose (5.14 mL/kg), Tanreqing low dose (2.57 mL/ kg). On the day of immunization, both Tanreqing groups were treated by intraperitoneal injection, with the PA group treated by intragastrical perfusion after T cell response, and the other groups treated with saline. Changes in body weight, neurological deficit score, incidence rate, mortality rate, and course of disease were observed for all mice. Brain tissue was isolated and stained with hennatoxylin-eosin, and pathological investigations performed to evaluate axon myelin damage by transmission electron microscopy (TEM). Myelin basic protein and microtubule associated protein-2 were analyzed by immunohistochemistry. RESULTS: Tanreqing injection significantly prolonged EAE latency and decreased the neurological deficit score, alleviated infiltration of inflammatory cells in the focus area, up-regulated hippocampal MBP expression at the acute stage and the remission stage, and increased microtubule associated protein-2 expression in the EAE brain to varying degrees in the acute stage. TEM analysis indicated that Tanreqing injection alleviates myelin damage in the EAE mouse and maintains the integrity of circular layer structures and alleviates axon mitochondrial swelling. CONCLUSION: Tanreqing injection alleviates EAE symptoms. (C) 2014 JTCM. All rights reserved.