Abstract： Objective To observe the expression of programed death-1 (PD-1) and its ligands including PD-L1 and PD-L2 in peripheral blood mono-nuclear cells (PBMCs) of patients with diabetic retinopathy (DR) patients.Methods Forty patients with DR (DR group) and 20 healthy controls (control group) were included in this study.There were 20 patients with non-proliferative DR (NPDR) and 20patients with proliferative DR (PDR).Peripheral Blood samples were obtained from two groups.Real time polymerase chain reaction (RT-PCR) was used to analyze PD-1,PD-L1,and PD-L2 mRNA expression in PBMCs.The clinical data was analyzed in DR group and controls,also in PDR group and NPDR group.Results The results of RT-PCR showed that the expression of PD-1 and PD-L1 mRNA in DR group were significantly lower than those in the control group (t=-2.060,-2.562; P=0.043,0.013).There was no significant difference in PD-L2 mRNA expression between DR and control group (t=-0.857,P=0.395).Compared with the NPDR group,the lower expression level of PD-1 mRNA and higher expression level of PD-L1 and PD-L2 mRNA in PDR group were observed,but the differences were not statistically significant (t=-1.335,0.987,0.131; P=0.190,0.334,0.897).Conclusion PD-1 and PD-L1 mRNA expression in PBMCs of DR patients is decreased compared with controls,but there are no differences in PD-L2 mRNA expression in them.