The research were conducted to determine the pellets degradation for different fill-in-degree of the rotating drum – from 15% to 30%. Measurements of the degradation coefficient was determined for the start and finally of cataracting in accordance with EN 15210-1: 2009 (E). The analysis of results showed the impact of the fill-in-degree, pellets type and velocity of the drum on the pellets degradation. When fill-in-degree increase pellets degradation coefficient decreased, but it is not exceeded according to the norm 2.5%.