Objective To investigate the alterations of cell- mediated immunity in patients with type 2 diabetes mellitus. Methods The level of CD3 CD4 CD8 in 30 normal subjects (NC group) and47 type 2 diabetes mellitus was measured by flow cytometry. Result Type - 2 diabetics had lower levels of CD4 and higher levels of CD8 than the non - diabetic control,especially during the 5 ～ 15 years of diabetes courses. The ratios of CD4 to CD8 was decreased. The correlation analysis showed that the level of CD3 CD4 CD8 and CD4/CD8 was not positively correlated with c - peptide. Conclusion Type - 2 diabeties have alterations of cell- mediated immunity.