Practical experiments were carried out to evaluate the performance of a locally manufactured grading machine for grading onion crop to increase product value, improve product quality and raise its export value. The main parts of the grading onion machine were as follows: feeding unit, grading unit, collection unit, chain and sprockets, and power source and transmission. The performance of the fabricated machine was studied according to the following parameters: Four different feeding rates of (0.9, 1.2, 1.5 and 1.8 Mg/h); three different inclination angles at horizontal level of (0, 5 and10°) for whole grading machine, and three different cylinder rotating speeds of (10, 20 and 30 rpm) corresponding to (0.25, 0.51 and 0.76 m/s), respectively. The performance of the fabricated machine was evaluated taking into account the following indicators: machine productivity, grading efficiency, mechanical damage percentage, energy consumed, operation cost and criterion cost. Experimental results showed that the suitable operating parameters for grading onions using the manufactured machine were: feeding rate of 1.8 Mg/h, cylinder rotating speed of 20 rpm and inclination angle of 10º, which recorded highest machine productivity, grading efficiency, acceptable mechanical damage percentage; minimum energy required and operational cost of 1.716 Mg/h, 95.3%, 11.6%, 0.33 kW.h/Mg and 10.03 L.E/Mg, respectively, also gave an acceptable criterion cost.