The effects of cooking Nigerian mango-seed kernels and seed replacement value for maize in broiler chicken rations were investigated. Day old broiler chicks were fed with diets containing 0% (control), 10% raw, 15%, 20% and 25% cooked mango kernels quantitatively substituted for maize over an eight week trial period. There was no significant difference (P> 0.05) in average daily feed intake, live weight gain, feed:gain ratio, nutrient retention, live and carcass weights, and dressing out percentage of birds placed on the control diet, diets with 10% raw or 15% and 20% cooked mango kernels. There was no significant effect (P> 0.05) due to diets on weights of head and internal organs, carcass ultimate pH, index of water holding capacity and percentage cooking losses of the birds. Twelve point five percent of broiler chickens placed on diets with 25% cooked mango kernels developed sprawl-legs and bow legs at seven weeks of age. Up to 20% of cooked mango kernels could be incorporated into boiler's rations without deleterious effect.