Chronic kidney disease (CKD) represents one of the most common complications of type 1 diabetes mellitus (T1D). Oxidative stress (OS) can be considered as a key link of pathogenesis of CKD associated with T1D, therefore, identification of the redox status markers is important for prevention of the development and progression of this disorder. The study aimed to assess the substances generated during oxidative destruction of proteins and their correlation with glomerular filtration rate (GFR) in patients with T1D and stage 1–3 CKD. The study involved healthy individuals (n = 14), patients with T1D showing no signs of CKD (n = 30), as well as patients with T1D and stage 1 CKD (n = 60), stage 2 CKD (n = 38), and stage 3 CKD (n = 31). Healthy participants were matched to the index group by age and gender: 42.9% were males, 57.1% were females, the average age was 30.6 ± 4.2 years; body mass index, systolic and diastolic blood pressure, lipid profile were within normal. It has been found that patients with T1D and stage 1–3 CKD demonstrate plasma accumulation of early and delayed neutral and base products of oxidative protein modification (OPM): spontaneous 157% based on median, metal-induced 143% based on median relative to healthy individuals. We have revealed a decrease in overall antioxidant status (OAS) of plasma in 51% of patients with T1D and stage 3 CKD compared to patients with T1D without CKD. Estimated GFR, the integral indicator of renal function, decreases with increasing plasma levels of OPM products, decreasing OAS. The data obtained allow us to consider plasma levels of OPM products, OAS as affordable and informative methods to assess progression of early stage CKD in patients with T1D.