OBJECTIVE： To study the imp rovement effects of Ganoderma lucidum polysaccharides crude extract on estradiol-induced thymus atrophy in mice. METHODS ：Totally 60 female ICR mice were randomly divided into normal control group（normal saline ），model group （normal saline ），G. lucidum polysaccharides crude extract high-dose and low-dose groups （400，100 mg/kg，by crude drug ），with 15 mice in each group. Except for normal control group ，other groups were given estradiol intraperitoneally （0.1 mg/mice，6 times）every other day to establish thymic atrophy model. The next day after modeling finished，they were given relevant medicine intragastrically ，once a day ，for consecutive 14 d. Twenty-four hours after last medication，organ（thymus，spleen）index，MDA content and GST activity in plasma were determined. HE staining was adopted to observe the pathological changes of thymus and spleen tissue in mice. The thymus cell apoptosis was examined by TUNEL assay ， and the T cell subsets in peripheral blood were detected by flow cytometry. RESULTS ：Compared with normal control group ，the thymus index ，proportion of CD 3+CD4+T cell in peripheral blood and CD 4+/CD8+ ratio were decreased significantly in model group （P＜0.01）；spleen index ，MDA content in plasma and thymocyte apoptosis level as well as the proportion of CD 3+CD8+T cell in peripheral blood were all increased significantly （P＜0.05 or P＜0.01）. Thymic cortex and medullary boundary of mice was blurred；the intercellular space was enlarged ；some cells were damaged and apoptotic in cortex ；no pathological changes were found in the spleen. Compared with model group ，thymus index and GST activity in plasma as well as proportion of CD 3+CD4+T cell in peripheral blood and CD 4+/CD8+ ratio were all increased significantly in G. lucidum polysaccharides crude extract high-dose group（P＜0.05 or P＜0.01）；while MDA content in plasma ，the apoptosis level of thymocytes were all decreased significantly （P＜0.01 or P＜0.05）；and the pathological changes of thymus were improved significantly. MDA content in plasma was decreased significantly in G. lucidum polysaccharides crude extract low-dose group （P＜0.01），and other indexes/pathological changes were not obvious. CONCLUSIONS ：High dose （400 mg/kg）of G. lucidum polysaccharides crude extract can improve the thymus atrophy induced by estradiol in mice.