The objective of the study was to compare the composition of organic acid and sugar of different mulberry cultivars and to evaluate the sweetness and acidity. The organic acid and sugar compositions of fruits from different 19 mulberry cultivars were analyzed by the HPLC method. The results showed that all cultivars contained citric acid, pyruvic acid, malic acid, succinic acid, oxalic acid, and fumaric acid, while several cultivars had lactic acid and acetic acid.The contents of organic acids ranged from 1687.9-2972.1mg/kg and Yunguo 1 cultivar and Anza 8 cultivar had the highest and lowest organic acids contents. Both fructose and glucose were soluble sugars in the mulberry. The contents of fructose and glucose of the same cultivars almost were equal. The fruit flavor index established by the ratio of sweetness and acidity could better reflect the real flavor of fruits than the sugar-acid ratio. Considering the flavor index of sweetness and acidity, the optimal cultivars were Baiyuwang and Taishen 1.