The legumes seeds - bean variety Herzfreier, lentil variety Lenka and oil seeds - poppy variety Amarin, rape variety Silesia and sunflower variety IBH-166 were chosen for investigation. Poisson's constant of the seeds is determined according to methodology by Kustermann et al. [2,3] and with the aid of machinery equipments at the Institut für Agrartechnik Universität Hohenheim - Germany. Using this method a great emphasis must be laid on the input data. Especially value of the force causing mechanical destruction of the seeds, entering the calculations, can be determined in various ways. Some of them are presented by examples. The results of the experiments •values of the force causing cracking of seeds, deformation of seeds, compressibility, elasticity coefficient and Poisson's constant are supplemented with the values obtained by the experiments with maize and spring and winter barley to make comparison.