Factors affecting the comminution of medium-volatile bituminous coal in a universal impact mill are rotor geometry, rotor speed and sieve opening geometry. Product properties like mean particle size and width of the product particle distribution are also influenced as well as energy efficiency. The result of comminution for medium-volatile bituminous coals and the universal impact mill used depends mainly on the geometry of the sieve openings and on the rotor speed. By changing the sieve opening geometry the width of the product particle size distribution can be influenced.