Difficulties in extraction and oil retention by oil-extracted seed meal have been recently observed in several oil plants. An assumption was made that the reason of these problems might be greater susceptibility of seeds to crushing due to differences in the seed microstructure. Changes in the seed microstructure might have resulted from drying in extremal conditions before they were supplied to oil plants. Mechanic properties and microstructure of rapeseeds were determined in the samples with strong diversified extractivity by means of agglomeration test. The results of this test were in agreement with the behaviour of seeds during industrial processing. A score was established for determining bad, medium, good and very good technological quality. Microscope studies of the seed structure (LM, TEM, SEM) revealed significant changes in the cotyledon cells of seeds with poor extractivity. In a model experiment with drying rapeseeds of various moisture at selected temperatures their mechanic properties were determined using agglomeration and modified oil-point tests. A highly significant effect of drying temperature was found on the microstructure changes, mechanic properties and technological usability of rapeseeds.