Background The aim of this study was to evaluate total antioxidant capacity (TAC) and biomarkers of lipid and protein peroxidation in the blood serum of dogs with benign prostatic hyperplasia (BPH). The study was conducted on 36 intact male dogs of various breeds. The dogs were assigned to two groups: BPH group (n = 18) and non-affected group (n = 18). Blood samples were collected from the cephalic vein. The antioxidant status of the serum was assessed using TAC. The levels of bityrosine, formylkynurenine and SH-groups were used as protein peroxidation biomarkers and the level of radical cations of N,N-diethyl-paraphenylene diamine (RC-DEPPD) was used as a marker for lipid peroxidation. TAC and the concentrations of SH-groups and RC-DEPPD in the serum were determined spectrophotometrically, the concentrations of bityrosine and formylokynurenine, were determined using spectrofluorimetric methods. Results The mean value of TAC in the serum was significantly lower (P = 0.01) in BPH dogs than in non-affected dogs (3.10 ± 0.56 vs 4.20 ± 1.60 μmol/g protein). Mean levels of protein and lipid oxidation biomarkers showed a trend towards oxidative imbalance, but there were no statistically significant differences between dogs with BPH and controls (P > 0.05). Conclusion In conclusion, significantly lower serum TAC in dogs with BPH compared to non-affected dogs suggests a potential involvement of oxidative stress in the pathogenesis of BPH in dogs. More studies are needed to clarify the role of oxidative stress in the development of BPH in dogs.