Grading of onion into size groups is often necessary in the food industry, to meet the requirements of some processing machines, or can be gradated as different grades according to the requirements of the market. The main objective of this study is to design, manufacture and evaluate the performance of grading prototype for onion based on the dimensions, which take place without physical contact. The prototype uses different successive operating components, such as photoresistor and actuators, each performing a specific task. Working principle of the grading prototype depend on the phototreistor, signal gathering circuit are also provided, a processing circuit and output circuit for distributing unit. When the onion bulb passes through the four sensors, it will shade the light signal sent by one or two or three or the four sensors according to bulb size, so the other sensors could not get the light signal, makes the sensors output voltage changes, the system receives digital signals produced by fruits that shadow the light from a photoresistor sensor during fruit measuring. After digital signals processed by the electronic circuit, every fruit's sizing level is deduced. Meanwhile, the control system will start to grade the bulb into a group according to bulb size, sending an executive order to the relative distributing motor to rotate for discharging this bulb to that group. Testing of the grading prototype was statistically factorial in completely randomized design, featuring three control factors (conveyor chain velocity, sphericity percentage of fruit and resting time) and three performance evaluation parameters (grading efficiency, damage percentage and productivity). The result showed that the best degree of grading efficiency obtained with the best degree of damage percentage were at 0.20 m/s chain velocity and 1.5 sec resting time. The best obtained values of grading efficiency were (85.25%) with (8.5%) damage fruit and 220 kg/h productivity. The energy required was 130.1 Watt/h. The cost of materials and manufacturing of the final grading prototype was 10000 L.E. The cost of grading prototype per hour was (4.912L.E).