The phenomenon of internal friction plays a major role in the majority of processing procedures. Thus, it is imperative to determine the internal friction coefficient for products under processing. It is not a simple objective in case of biological materials for which application of classic friction definitions is rather limited. The studies presented aimed at determination of the impact of selected factors on the internal friction value of rye and wheat grains. The measurements were taken on an original measuring equipment. The analysis of obtained results enabled to categorize three motion phases of grain layers shifted toward each other. The statistic tests performed proved that for the both cereals there was a correlation among the studied parameters.