The concentration of sucrose,glucose,fructose,titratable acid,ABA and the activity of acid invertase(AI)were measured injuice sacs of Bendizao mandarin(Citrus succosa Hort),Ponkan(Citrus reticulata Blanco),Miyagawa wase(Citrus unshiu Marc)and Meyer lemon(Citrus,meyeri Y).The acid hydrolysis of sucrose in vitro was also studied.The results showed that the sugar content,the ratio of different sugars,titratable acidity,ABA content and the activity of AI were obviously different in four citrus varieties.The sugar content inj uice sacs of citrus fruit was related to that of ABA at the late stage of fruit development.The result suggested that ABA played an important role in sugar accumulation in juice sacs of citrus fruit.Bendizao mandarin and Miyagawa wase mainly accumulated sucrose inj uice sacs of citrus fruit.Meyer lemon accumulated hexose,and Ponkan citrus was the sucrose-hexose accumulating type variety.In Meyer lemon with high acid degree,the composition of sugar inj uice sacs was determined by acid-hydrolysis of sucrose.In Bendizao mandarin,Ponkan citrus and Miyagawa wase with low acid degree,the composition of sugars at the late stage of fruit development was obviously affected by the AI activity.