The aim of the present work is developing of the performance of cutting knives in crop residues shredder. The items to achieve the aim of the present study are: (1) Study of some physical and mechanical properties of cotton stalks and rice straw. (2) Evaluation of shredder performance and cutting knives before and after development.(3) production of cutting knives from local materials. (4) Development of cutting knives. (5) Chopping machine cost. The performance of chopping machine was tested under the following parameters: A-    Four cutter speeds (900, 1050, 1200 and 1500 rpm), B-    Three different moisture content (30.0, 40.0 and 50.0 %) and (22.0, 25.0 and 30.0% , w.b.) for cotton stalks and rice straw, respectively. C-    Two different types of shapes cutting knives {smooth-edge (Original knives) and serrated-edge (Modified knives)}. The final results of this study could be summarized as follows:- Generally by increasing the cutter head speed from 900 to 1500 rpm tends to increase percentage of cutting length   >2cm from (86.2 to 90.6%) and (83.8 to 87.0%), chopper productivity from (1.10 to 1.70 Mg/h) and (1.00 to 1.50 Mg/h), degree of destruction from (42.5 to 53.0 %) and (29.0 to 35.0%), useful power from (1.19 to 3.05 kW) and (1.10 to 2.80 kW) and unit energy from (1.88 to 1.79 kW.h/Mg) and (1.10 to 1.87 kW.h/Mg) for cotton stalks and rice straw, respectively, with machine before modification at moisture content of 30.0 % and 22.0 % (w.b.) for cotton stalks and rice straw, respectively and type of cutting knives smooth-edge (Original knives). Also, increased percentage of cutting length > 2cm from (91.7 to 94.5 %) and ( 85.7 to 89.5 %), chopper productivity from (1.30 to 1.80 Mg/h) and (1.20 to 1.60Mg/h), degree of destruction from (50.9 to 72.5 %) and (45.4 to 60.8%), useful power from (1.10 to 2.70 kW) and (1.00 to 2.20 kW) and  unit energy from (0.85 to 1.50 kW.h/Mg) and (0.80 to 1.40 kW.h/Mg) with machine after modification at moisture content of 30.0 % and 22.0 % (w.b.) for cotton stalks and rice straw, respectively, and type of cutting knives serrated-edge (Modified knives).