One of the causes of the occurrence of mechanical damage to seeds during harvest and other technological processes is the effect of impact forces acting during the contact of seeds with moving elements of agricultural machinery. Seeds of winter rape cv. Californium and Bazyl and of spring rape cv. Start, and kernels of winter wheat cv. Rysa, Zawisza and of spring wheat cv. Jasna were subjected to the of impact forces. The effect of the seed and kernel moisture on the extent of impact damage was studied. The study was conducted under laboratory conditions, on a test stand designed at the IA, PAS, in Lublin. It was found that the relation between seed/kernel moisture content and impact damage was non-linear, and that there exists an optimum moisture level at which the minimum damage occurs under the effect of impact forces.