Onion bulbs are graded manually at farm and trader level.Manual grading of onion is a labour consuming and tedious operation coming with many losses. Therefore, the modern technologies, like automatic grading systems, are of utmost need. Grading is one of the most important operations affecting onion export. It determines the size of standard sale package, thereby increasing marketing attractiveness, and simplifies the mechanization of different handling systems, such as cutting and peeling. There are different types of onion graders available in the Indian market. These are of higher throughput (10 to 12 t/h) and highly expensive (costing Rs 10 lakh or more). Hence, they are not being used at the farm level as it is beyond the reach of ordinary farmers having small land holding who are growing onion crop. This necessitated to develop an efficient low cost grading machine for onion. The onion should be graded in the divergent rollers type onion grader at 15 rpm roller speed having 8 degree roller inclination to obtain the optimum grading efficiency, i.e., 82.98 per cent on weight basis and 85.25 per cent on number basis. At the optimized conditions, the capacity was 601.38 kg/h.