Aim: To determine if oxygen saturation in retinal vessels depends on the degree of diabetic retinopathy. Material and methods: A prospective study comparing values of oxygen saturation in retinal arteries, veins, and arterio – venous (A-V) difference in healthy persons and in patients with diagnosed diabetes. The study included 114 eyes of 76 patients with diagnosed diabetes, and 57 eyes of 57 patients without diabetes as a control group. Results: The average retinal arterial saturation in patients without diabetes was 96.5 ± 2.6 %, and increased in patients with severe non-proliferative or proliferative diabetic retinopathy to 100.5 ± 5.6 %. The average venous saturation in patients without diabetes was 62.3 ± 7.4 % and increased to 74,0 ± 7.2 % in patients with severe non-proliferative diabetic retinopathy. Conclusion: In patients with diabetic retinopathy, we confirmed the increase of hemoglobin oxygen saturation as in the arterial as in the venous blood in retinal vessels; and significant decrease of arterio-venous difference according to the severity of diabetic involvement was confirmed as well.