This review focuses on the biochemical mechanisms of oxidative damage to sperm, the role of antioxidants, as well as the clinical consequences of supplementation for the improvement of sperm fertility. There is growing interest in dog breeding and in methods of maintaining semen quality for natural mating or artificial insemination (AI). Canine sperm are sensitive to oxidative damage. Semen contains endogenous, enzymatic, renewable, and non-enzymatic, and non-renewable antioxidants. However, the excess of reactive oxygen species (ROS) or depletion in antioxidative defense may lead to oxidative stress, causing damage to sperm cells and a decrease in fertility. The possible way to maintain sperm cell fertility potential is supplementation of diet and/or semen extenders with antioxidants. It seems that oral antioxidant supplementation improves the oxidative status and quality of semen and may have a positive effect on the fertility of male dogs with reproductive problems. Many studies point to the potential role of antioxidant supplementation in extenders in protecting canine sperm from oxidative damage during processing. However, only a few studies have assessed the fertilization capacity of supplemented sperm after AI. Intensive studies, including the examination of pro- and antioxidative properties of dog semen as well as the role of antioxidant supplementation to dogs and semen extenders, should be performed, as it is a serious market and breeders need. The results should be related not only to semen analysis but pregnancy rate as the best marker of fertility. Nevertheless, the use of antioxidants in the supportive treatment of fertility disorders in male dogs to improve semen quality and their addition to dog semen extenders to preserve sperm fertility appears to be reasonable.