Objective To study the humoral immunity status and distribution pattern of lymphocyte subgroups of peripheral blood mononuclear cell (PBMC) in patients with Kaschin - Beck Disease (KBD), and their relationship with erythrocyte selenium. Methods 23 X- ray diagnosed patients, 22 age- and sex- matched healthy children in KBD affected area (KAA), And 25 in KBD non- affected area (KNAA) were randomly selected. Immunohistochemistry with monoclonal antibodies anti - CD4, anti-CD8. anti - CD20 was conducted to analyze the lymphocyte subsets. Serum IgM, IgA, IgG, Complement C3 and C4 were assayed using rate nephelometry (Array 360 System, USA). The contents of erythrocyte selenium was determined by 2,3 - diaminonaphthalene fluorescence assay. Results CD4+ and CD8 + cells percentage in PBMCs and serum IgA were significantly lower in KAA than those in KNAA( P ＜ 0.05). CD20 +percentage in KAA displayed a decreasing trend compared to KNAA, although not statistically significantly. No statistical differences were found in CD4/CD8 ratio, serum IgG, IgM, C3 and C4 levels. Erythrocyte selenium level in KAA still showed a pronounced decrease compared to that in KNAA. Correlation analysis showed that erythrocyte selenium contents had a strong association with the CD4 cell percentage ( r =0.625, P ＜0.05), and also a close relationship with serum IgA ( r =0.462, P ＜0.05). In addition, we detected a moderate correlation between the serum IgA and CD4 + percentage ( r = 0. 130, P ＞ 0. 05). Conclusion Taken together, our resalts suggested that children in KAA had a comparably low cellular immunity level manifested by the marked depression of CD4 and CD8 cells percentage, and their humoral immunity status was also in a state of moderate immune suppression. Of this immune disorder in KBD patients, selenium deficiency probably played a critical role via affecting the distribution pattern of peripheral blood lymphocyte. Selenium-deficiency and immune impairment maybe both have something to do with the cause - effect chain of KBD.