OBJECTIVE: To study the effect of oxymatrine on pathological change in brain tissue of newborn mice infected by cytomegalovirus (CMV). METHODS: CMV of TCID50 was inoculated into the brain of the newborn mice, and the morphological change in the brain tissue infected by CMV was observed with light microscope and transmission electron microscope. RESULTS: In the model control group, the results showed that there were some inflammatory cellular infiltration and focal necrosis in the brain tissue of newborn mice infected by CMV. The ultrastructure change in the brain tissue showed that the nuclear membrane of cerebral neurons sunk, the chromatin deformed and fused into masses, the cytoplasm vacuolated, the endoplasmic reticulum disarranged and the Nissl's body was blurred or disappeared. After being treated with oxymatrine (50 mg/kg, ip) for 15 days, those pathological changes of the brain tissue in the newborn mice could be significantly improved. CONCLUSION: Oxymatrine has an obvious inhibition on CMV in vivo.