The article deals with the optimization of cleaning grains and seeds of agricultural crops from weed seeds. The process of cleaning grain material by one-dimensional horizontal vibrations depends on the friction coefficients of the seeds against each other. It is optimized by selecting the amplitude and angle, relative to the vertical, under which the cylindrical container containing the grain mixture is located. Experiments were carried out with almost all types of seeds most widely used in the domestic agricultural industry. The cleaning process was investigated only at amplitudes smaller than the seed size. The seeds of cultivated plants and weeds move upward or downward, depending on the specific gravity. Calculations show that with correctly selected values of the amplitude and angle, the average trajectories of the grains are practically straight lines parallel to the generatrix of the cylinder containing the seeds. Studies have shown that the maximum cleaning speed is achieved under the condition that the angle of inclination of the cylindrical vessel is equal to the natural slope of the seeds with the highest specific gravity.