Onion seeds are microbiotic seeds and loose their viablility over the period of three months. This leads to certification hindrances and economic losses for farmers. Seed quality enhancement of such seed is of requisite, among the different enhancement techniques the economical, ecological, effective and easy to handle magnetic field, seems to be promising in modern agriculture. Hence the experiment was conducted at Department of Seed Science and Technology, UAS Dharwad in the Kharif of 2023 to understand the effect of magnetic field on seed quality and biochemical parameters of aged and medium vigour onion with 72 per cent germination. Methodology consisted of subjecting the aged onion seeds (6 months old) of variety Bheema Super to magnetic field of different intensities and time periods and were compared with untreated control. Data was analysed using CRD with three replications. Amongst the magnetic field, 60mT for 30 min was found to be best with enhanced seed quality and biochemical parameters where the germination increased by 12 percent, speed of germination by 54.19 percent, total seedling length by 65.53 percent and catalase activity by 47.47 percent as compared to control. Moreover the optimum dose was able to maintain the minimum standard of germination of 70 percent upto 9 months. Deleterious effects on seed quality were observed at high intensities of magnetic field. It has been found the effectiveness of magnetic field depends on magnitude as well as duration of exposure. Hence magnetic field can be successfully used to improve the quality of marginal quality seeds of onion.