Rye-grass (Lolium multiflorum var. westerwalidicum) is one of the basic seed grass varieties. Investigation on physical features of seeds, especially geometrical and aerodynamical properties follows adaptation of combine-harvester to grass harvesting. Geometrical properties (length, width) was measured by optical apparatus, which gave 29.7-fold enlargement of perpendicular projection of investigated seed. The biggest area of the projection was measured as lifting surface. Length and width of seed were from the contour of lifting surface. Aerodynamical properties was measured by apparatus, which construction made possible a fluent regulation of air stream velocity. Relative wind coefficient arise from critical velocity. All quantities were presented as statistical distribution, furthermore aerodynamical properties: critical velocity, resistance coefficient and relative wind coefficient were presented in function of mass and dimensions of seed.