AIM: To detect the possible role of interleukin (IL)-26 in diabetic retinopathy (DR) patients. METHODS: Subjects were divided into diabetes without retinopathy (DWR) group (n=20), non-proliferative diabetic retinopathy (NPDR) group (n=20), proliferative diabetic retinopathy (PDR) group (n=20) and normal control group (n=20). The protein expression of IL-26 in the serum and vitreous fluid were measured by enzyme-linked immunosorbent assay (ELISA). The mRNA change of IL-26 in peripheral blood mononuclear cells (PBMCs) was assessed by real-time polymerase chain reaction. RESULTS: The serum expression of IL-26 in PDR group was significantly elevated compared with the normal control group, DWR group and NPDR group. The vitreous fluid concentration of IL-26 in PDR patients (without anti-VEGF therapy) was also higher compared to normal controls. However, no obvious significance was found concerning the expression of IL-26 in vitreous fluid between PDR after anti-VEGF therapy and normal controls. In PDR group, the mRNA level of IL-26 significantly increased compared with the normal controls and DWR patients in the PBMCs. CONCLUSION: Protein and mRNA expression of IL-26 are increased in serum, vitreous fluid and PBMCs in PDR patients, suggesting that IL-26 may be associated with the pathogenesis of PDR.