Production and utilization of Allium cepa is the basis of nutritional value and the human health maintainance. The review discusses the main onion biologically active compounds, determining the biological activity of this vegetable, peculiarities of antioxidant and carbohydrate distribution between inner and outer scales, changes in the content and distribution of biologically active compounds and chemical elements in conditions of various abiotic stresses: high temperature, drought, flooding and heavy metal loading. Factors affecting onion pungency and natural antioxidant distribution are included. Special attention is payed to sulphur derivative alkenyl cysteine sulphoxides, and polyphenols and flavonoids, sterols, fructoolygosaccharides, organic acids, amino acids, and minerals. Onion selection on tolerance to the unfavorable environmental factors is discussed. The presented data may be the basis for the direct production of Allium cepa with high yield and valuable nutritional characteristics.