Abstract: Compounds or substances which act to reduce nutrient intake, digestion, absorption and utilization and may produce other adverse effects are referred to as antinutrients or antinutritional factors. Seeds of legumes and other plant sources contain in their raw state wide varieties of antinutrients which are potentially toxic. The major antinutrients includes: toxic amino acids, saponins, cyanogenic glycosides, tannins, phytic acid, gossypol, oxalates, goitrogens, lectins (phytohaemagglutinins), protease inhibitors, chlorogenic acid and amylase inhibitors. These antinutrients pose a major constraint in the use of plant protein sources in livestock feeds without adequate and effective processing. The level or concentration of these anitnutrients in plant protein sources vary with the species of plant, cultivar and post-harvest treatments (processing methods). This paper reviews the nutritional effect of major antinutrients present in plant protein sources.