The sharpener unit attached to the chopping machine used for maize crops has a substantial effect on knife sharpness and chopping speed, which in turn affects machine productivity, chopping length, chopping efficiency and specific energy requirements. The machine was tested at four chopping speeds, which were 1650, 1900, 2150 and 2400 rpm (47.52,54.72,61.92 and 69.12 m s^-1), and at three crop moisture content levels, which were 60, 70 and 77 %. The results showed that the performance of a sharpener unit attached to a maize chopping machine is better than a maize chopping machine without an attached sharpener unit in terms of productivity, chopping length, chopping efficiency, and energy efficiency. At a constant clearance of 10 mm, an optimum moisture content of 70 %, and an optimum knife speed of 2150 rpm (61.92 m s^-1), the results showed that the maize chopping machine with a sharpener unit yielded a productivity of 5.74 t h^-1, a chopping length of 15 mm, a chopping efficiency of 79.37 %, a specific energy requirement of 3.42 kW h t ^-1 and operating cost of 35.82 LE t ^-1