AIM: To determine the relationship between proliferative diabetic retinopathy (PDRP) and plasma coenzyme Q10(CoQ10) concentration.METHODS: Patients with type 2 diabetes and PDRP were determined to be the case group (n=50). The control group was consist of healthy individuals (n=50). Plasma CoQ10 and malondialdehyde (MDA) levels were measured in both groups.RESULTS: Ubiquinone-10 (Coenzyme Q10) levels in PDRP and control subjects are 3.81±1.19μmol/L and 1.91±0.62μmol/L, respectively. Plasma MDA levels in PDRP and control subjects were 8.16±2μmol/L and 3.44±2.08μmol/L, respectively. Ratio of Ubiquinol-10/ubiquinone-10 in PDRP and control subjects were 0.26±0.16 and 1.41±0.68, respectively.CONCLUSION:The ratio of ubiquinol-10/ubiquinone-10 is found lower in patients with PDRP. High levels of plasma ubiquinol-10/ubiquinone-10 ratio indicate the protective effect on diabetic retinopathy.