The scarce fertility of the cryopreserved equine sperm has significantly limited its use in reproducti ve biotechnology. Oxidative stress is one of the facts that are related the most to this phenomenon, due to the increase in the levels of species that react to oxygen in the sperm as a result of the thermal shock, the toxicity of cryoprotectors and the alteration in the disposal and the functionality of the endogenous antioxidants during cryopreservation. This revision article analyzes the effect of oxidative stress on the