In order to collect weed seeds while harvesting with a combine it is necessary to know their aerodynamic properties, because separation of grain and chaff in a combine is mainly done by air. Terminal velocities or other aerodynamic characteristics of weed seeds are rarely tested and little found in literature. Twenty different weed seeds were tested. Terminal velocities were determined with an Automatic Test Stand. Tested were seeds, which are important in European grain-cultivating. The seeds are from: Alopecurus myosuroides, Apera spica-venti, Avena fatua, Atriplex patula, Capsella bursa-pastoris, Chenopodium album, Cirsium arvense, Convolvulus arvensis, Galeopsis tetrahit, Galium aparine, Lamium purpureum, Matricaria recutita, Myostis arvensis, Polygonum convolvulus, Rumex crispus, Sinapis arvensis, Sonchus asper, Stellaria media, Thlaspi arvense, Veronica persica, Viola arvensis. Of some seeds terminal velocities were tested at different moisture contents.