. The frictional properties of processed materials and their relationships with other parameters have to be determined to optimize production. In this study, the dimensions and mass of basic cereal seeds (wheat, rye, barley, oats, and triticale) and their external friction angles on a steel surface were determined for four seed orientations. Frictional properties were determined with two optoelectronic modules that measured the angle of static friction and the time required for a seed to travel across a given distance. The results were used to calculate the coefficient of sliding friction. Each seed was described with four shape factors and density variables. The relationships between the measured parameters were determined in an analysis of variance and a correlation analysis. The orientation of the hilum and crease relative to the steel surface significantly influenced the coefficient of static friction of the analyzed seeds. The lowest values of that coefficient were noted for seeds positioned with the crease up and the hilum down, and the highest values were found for seeds positioned with the crease down and the hilum up. The coefficient of sliding friction was determined in the range of 0.13 to 0.23, and it accounted for 39.5% and 64.3% of the value of the coefficient of static friction, respectively. Seed dimensions, seed mass, calculated shape factors, and seed density did not influence the coefficients of static and sliding friction. The coefficient of static friction was correlated mainly with seed thickness, and the coefficient of sliding friction was correlated with seed width.