A field experiment was carried out during the two successive winter seasons of 2020-2021 and 2021-2022, in the private vegetable farm at Diarb Negm District, Sharkia Governorate, Egypt, to study the effect of mineral nitrogen levels and plant density on fresh weight, total N, P, and K uptake, total yield, nitrogen use efficiency, and bulb quality of the onion (cv. Ahmar tantawy). This experiment included 12 treatments, which were combinations between four levels of mineral nitrogen (0, 192, 240, and 288 kg N/ha) and three plant densities (4, 5, and 6 rows per ridge, equalling 33.33, 41.67, and 50 plants per m2, respectively). These treatments were arranged in a split-plot design with three replications. Nitrogen levels were randomly arranged in the main plots, and plant densities were randomly distributed in the subplots. The interaction between nitrogen levels at 288 kg N/ ha and plant density (4 rows/ridge) gave the highest values of fresh weight of leaves, bulbs, and total fresh weight/plant, percentages of the yield of grade 1, grade 2, and exportable yield from total yield, and increased total N, P, and K uptake by the plant, total carbohydrates, total sugars, and vitamin C contents in bulbs. The interaction between N at 244 kg/ha and high plant density (6 rows/ridge) increased total yield per hectare and nitrogen use efficiency in onion plants.