The present investigation was carried out at Kafr El-Hamam, Sharkia Governorate, Egypt during 2018/2019 and 2019/2020 seasons to investigate the effect of onion density intercropped with sugar beet on the productivity of the two crops, competitive indices, net returns and root rot incidence of sugar beet. The treatments were arranged in randomized complete block design with three replications. The experiment included 6 treatments: one, two, three and four rows of onion intercropped with sugar beet as well as solid sugar beet and onion. Solid sugar beet gave the highest root diameter and the lowest purity (%) in the two seasons. Also, it gave the highest value for each of studied trait as compared with intercropped sugar beet in one season. Solid onion (T2) gave the highest values in onion yield and the studied traits followed by T4. Yield components of onion intercropped with sugar beet were decreased by increasing onion row number. The highest LER and net return were obtained with intercropping two rows of onion between sugar beet rows meanwhile, the lowest LER was recorded by intercropping four rows of onion. Intercropping onion decreased root rot (%). It is recommended intercropping two rows of onions on the middle terrace, 10 cm between hills and 15 cm between the two rows: with sugar beet which were growing in both sides of terrace 120 cm width, this system gave the highest value for each of rate of yield, LER, net income and reducing root rot (%) without using chemical methods.