Abstract: An agent for increasing the sugar content and/or decreasing the acid content of plant fruits has as a substantial main component thereof a fluorine-containing .beta.-indolebutyric acid compound represented by the general formula ##STR1## (wherein Y stands for one member selected from the class consisting of hydroxyl group, alkoxy group, amino group, and alkyl amino group and R.sup.1 and R.sup.2 independently stand for one member selected from the class consisting of hydrogen atom, halogen atom, alkyl group, alkoxy group, aryl group, nitro group, amino group, and alkyl amino group). A method for producing ripe fruits having a high sugar content and/or a low acid content by causing the fluorine-containing .beta.-indolebutyric acid compound mentioned above to adhere to unripe fruits on plants and plants bearing fruits and subsequently allowing the fruits to mature.