Abstract: Fats or lipids are the excellent and easily digestible source of energy, and feeding horses diets supplemented with oils is a relatively new trend in the horse nutrition research. Horses are non-ruminant herbivores（hind-gut fermentors）. Normal horse rations contain only 3 % to 4 % fat, however, horses can digest up to 20% fat in their diet. The fats in horse diets mainly relates to the content of Omega-3 and Omega-6. Most types of vegetable oils and some types of animal oils like fish oils could be the supplementation of feeding horses. This paper summarized characteristics of digestion process and oil digestion in the horses and the effects of supplementation of oils in the diets on reproductive performances of mares and stallions, suggesting that feeding oils had positive effects on the sperm quality of fresh semen, cooled semen, frozen-thawed and shipped semen of stallions, and feeding oils to broodmares may alter the lipoprotein profile in the blood, thus affecting the synthesis of the endocrine compounds involved in regulation of reproduction. Moreover, there is some indication that feeding fat-supplemented diets to lactating broodmares may increase the concentration of fat in milk, and their foals would grow faster compared to their counterparts which were fed conventional low-fat diets.