Crop residues are considered among the most important materials in Egypt, e.g. especially cotton stalks, corn stalks and rice straw. There are many types and makes of the imported choppers to Egypt to assist in recycling the field crop residues. One of the chopper machines which are imported have many problems such as size of cut and throwing cut materials outside the machine. The present research work was conducted at Gimaza research station, Gharbia Governorate to test the machine performance before and after modification. The main objectives of this study were: 1- Testing and evaluating the chopper (original type). 2- Modifying and redesign the machine to improve the thrower operation, power transmission, the efficiency and increasing the productivity. 3- Producing and fabricating the machine after modification locally. 4- Testing and evaluating the chopper machine after fabrication. The modified machine was fabricated from local materials at a private sector company (Tanta motors). The cutting drum was modified, 32 flail knives were mounted on the circumference of a pipe drum (18 cm diameter). The overall drum diameter was 56 cm. The thrower fan was also modified to have direct central suction (centrifugal fan). The main results of the machine capacity before modification were: 484.6 kg/h and 625 kg/h (max. machine capacity) for cotton stalks and corn stalks, respectively at 3500 rpm drum speed. The max. chopping power required was 15.5 kW (21 hp) and 13.4 kW (19 hp) for cotton and corn stalks, respectively. The air speed was not enough at all tests to throw the cutting material outside machine duct, so the rear plat (concave cover) was moved through tests. The modified locally manufactured machine was tested with cotton stalks, corn stalks and rice straw. The results were improved with cotton and corn stalks and the machine was successful with rice straw. The main capacities were as follows: 1200, 800, 1224 kg/hr (max. machine capacity) for cotton stalks, corn stalks and rice straw, respectively at 3500 r.p.m chopping drum speed. The maximum chopping power requirements were 25.98 kW (35.35 hp), 22.98 kW (31.27hp) and 24.29 kW (33.05 hp) for chopping cotton, corn stalks and rice straw respectively. The size of the cut materials varied between 1.4 mm to 300 mm before modification and between > 0.71 mm to 30 mm after modification.