Polyphenol and phytic acid contents of wheat, maize and sorghum varied significantly and increased progressively with the levels of grain infestation (25, 50 and 75%) caused by Trogoderma granarium Everts and Rhizopertha dominica Fabricius separately and mixed population. Higher insect infestation (50 and 75%) of wheat and sorghum led to substantial increase (by weight) in polyphenol and phytic acid due to the selective feeding activities of the beetles. Feeding of both insect species on maize caused proportional increase in polyphenol but decrease in phytic acid due to variation in the distribution of these compounds in seed components and also selective feeding habit of insects. Storage of uninfested cereal grains for up to 4 months did not cause appreciable change in the levels of these antinutrients