The contents and their seasonal changes of non-volatile organic acids and sugars of various fruits in Korea, apricot(maesil), peach, grape, apple and pears were measured. The organic acid contents were determined by gas chromatography and the free sugars were detected by thin layer chromatography. The results were as follows: 1) The common non-volatile organic acids found in those fruits were oxalic, fumaric, succinic, maleic, tartaric and citric acids: though their contents varied from almost none to 3430mg/100g. 2) Malic acid was contained in all above fruits with generally the highest contents ranging $18{sim}3430mg/100g$ among different fruits. In every fruits oxalic was the least contained among other organic acids, almost none to trace except apricot(maesil) which contained 10.8mg/100g. 3) It seemed that generally all the non-volatile acids contents decreased after ripening except maleic acid and the cases of an apple and a pear varieties where they increased. 4) Glucose and fructose were detected in all fruits both matured and unripened by thin layer chromatography. Maltose was found in apricot(maesil), peach, grape and apple. Sucrose was detected in apricot(maesil), peach, grape, apple and pear.