In the years 2003-2005 a study was conducted on the basic properties of spring rape seed, cv. Star, and of seed of two compound hybrids – Margo and Jura. Determinations performed for the seed in bulk included seed layer porosity, WTK (weight of thousand kernels), density, and angles of slide and of repose. Determinations for individual seeds included seed diameter (thickness), and resistance to static load in a compression test on the Instron strength tester. The strength tests pro-vided the following mechanical parameters of the seed: values of maximum force and strain causing structural damage, force and strain within limits of elasticity, and values of energy (work) causing destruction of seeds. In the first year of the study, measurements were made for 10 levels of rape seed moisture (6-24%, at 2% increments). In subsequent years, measurements were made for air-dry seeds. It was found that with increasing seed moisture there was an increase in seed layer porosity, WTK, and in the angles of slide and of repose, while seed density decreased. Diameters of individual seeds did not change up to seed moisture level of 22%. Values of maximum force de-creased with increasing seed moisture, while values of strain increased. The highest values of force within limits of elasticity and the corresponding strain occurred at seed moisture within the range of 12-14%. Also, the study revealed cultivar-related differences as well as differences between the years of the study.