Onions are widely grown in Vietnam, with many different varieties ofonions. Each onion variety has different colour characteristics, and the ratio ofnutritional ingredients is also different. The aim of this study is to determine somenutritional components of onions to serve as a scientific basis for the application ofappropriate processing methods. The following was determined for each cultivar: thecontent of macro- and micronutrients, reducing and total sugar, and the vitamin Ccontent. Significant differences in chemical composition between the analyzedcultivars were found. The cultivars of the same colour exhibited similar tendenciesin terms of accumulating most of the analyzed elements. The greatest differences inthe chemical content were found among yellow and red cultivars. Yellow cultivarsaccumulated significantly greater amounts of nitrogen, phosphorus, potassium,magnesium, iron, manganese, zinc, copper, and reducing sugar than red onioncultivars. Red onion cultivars contained significantly greater amounts of total sugarand vitamin C than yellow onion cultivars.Onions are widely grown in Vietnam, with many different varieties ofonions. Each onion variety has different colour characteristics, and the ratio ofnutritional ingredients is also different. The aim of this study is to determine somenutritional components of onions to serve as a scientific basis for the application ofappropriate processing methods. The following was determined for each cultivar: thecontent of macro- and micronutrients, reducing and total sugar, and the vitamin Ccontent. Significant differences in chemical composition between the analyzedcultivars were found. The cultivars of the same colour exhibited similar tendenciesin terms of accumulating most of the analyzed elements. The greatest differences inthe chemical content were found among yellow and red cultivars. Yellow cultivarsaccumulated significantly greater amounts of nitrogen, phosphorus, potassium,magnesium, iron, manganese, zinc, copper, and reducing sugar than red onioncultivars. Red onion cultivars contained significantly greater amounts of total sugarand vitamin C than yellow onion cultivars.