A rice straw milling unit manufactured in local workshop and the experimental evaluation was carried out in rice straw assembly station. The obtained result data indicated that the manufactured rice straw unit created solutions for all the problems faced the regular hammer mill machines in dealing with rice straw. The operation parameters under investigation and evaluation were air suction velocity of (1.97, 3.61, 5.37 and 6.91m/s), Number of hammers (54, 81 and 108 hammers) and Hammers thickness (2 and 5mm).The obtained results were for production the very low milled rice straw particle size applications such as MDF, papers making, silica jell and ethanol production must use air suction velocity of 5.37 m/s with number of hammers of 108 hammers with hammer thickness of 2mm. As this operation parameters obtained the following results 1.17 Mg/h main production rate in first cyclone, 43.95 kg/h, very fine product (straw dust) in second cyclone , 29.17 kW.h/Mg specific energy (SE), 153.63kg/m3 milled straw bulk density,0.43% losses in machine chamber, 1.93%losses with air blower output and particle size distribution  percentage of 36.41% , 25.97% and 9.33% for particle size of (<2.00->1.00mm), (<1.00->0.60mm) and (<0.60mm) respectively. The results showed also for milling the rice straw as raw material for animal feed pellets or bio fuel as thermal energy better use air suction speed of 5.37m/s , 54 hammers number with 2mm hammer thickness, this operation parameters obtained the following results 0.83 Mg/h main production rate in first cyclone, 32.45 kg/h very fine product (straw dust) in second cyclone , 32.18kW.h/Mg specific energy (SE),112.29kg/m3 milled straw bulk density,5.94% losses in machine chamber, 1.23 %losses with air blower output and particle size distribution percentage of 32.43% ,37.07% for particle size of (<3.75- >2.80mm) and (<2.80- >2.00 mm) respectively.