The possibility of producing a new type of vinegar from worthless onions, which fail to meet the quality standards required for marketing, was investigated. Several kinds of onion were initially tested as raw material for vinegar production, and vinegar was successfully produced from the juice of a red onion, the cultivar Kurenai, by batch culture using yeast and Acetobacter aceti. Nutritional analysis revealed that the potassium content of onion vinegar was extremely high, white the amount of sodium was lower than that in conventional vinegars. It was also shown that the total amino acid and total organic acid contents of the onion vinegar were respectively 1.6-6.9 times and 3.5-11.5 times those in other kinds of vinegars.