For the ultimate manufacture of vinegar with watermelon juice, we examined the preliminarily alcoholic fermentation of watermelon juice using Saccharomyces cerevisiae, Saccharomyces cerevisiae var. ellipsoideus and Kluyveromyces fragilis. The juice contained 3.2% total reducing sugar by the Somogyi-Nelson method. Strains of yeast culture, pH, temperature and concentration of sugar in the juice were important factors affecting alcoholic fermentation. Saccharomyces cerevisiae var. ellipsoideus produced 5.3% alcohol from the juice fortified with 12% glucose under the conditions of pH 5.73 and 27℃ for 8 days. Generally, small quantities of various salts and N-sources affected little the alcoholic fermentation of the juice. The sterilization of the juice by autoclaving improved efficiency of fermentation than that by SO₂ sterilization. Determination of alcohol was carried out by the gas chromatographic method using Chromosorb W: Carbowax as packing material.