The experiments of this study were carried out during the agricultural seasons of 2007/2008 and 2008/2009 at a private mill for milling grains in Abou Kbeer district, Sharkia Governorate to optimize some operating parameters affecting the performance of a prototype hammer mill. The performance of hammer mill was evaluated under different parameters including drum rotational speed, grain moisture content, hammer thickness and concave clearance. The performance of hammer mill was evaluated taking into consideration hammer mill capacity, efficiency, particle size distribution (fineness degree), power, energy requirement and operational cost. The obtained results reveal that it is recommended to use the hammer mill at drum rotational speed about 2250 rpm (33.56m/s),grain moisture content of 10%,concave clearance of 5mm and hammer thickness of 5mm to produce pelleting feed by increasing the percentage of fine milled corn (FMC) and decreasing coarse milled corn (CMC). Producing mash feed for commercial use can be achieved by using the mill at drum rotational speed about 1550 rpm (23.85m/s),grain moisture content of 14%,concave clearance of 12mm and hammer thickness of 1.5mm by decreasing percentage of fine milled corn (FMC) and increasing coarse milled corn (CMC) and medium milled corn (MMC).