The first KI-catalyzed direct acyloxylation of indolin-3-ones with carboxylic acids has been developed using 30% aq. H₂O₂ as a green oxidant at room temperature. Through this strategy, various C2-acyloxy indolin-3-ones were obtained in up to 96% yield. Moreover, the C2-acyloxy indolin-3-ones can serve as versatile intermediates for the synthesis of nucleophilic 2-monoarylated indolin-3-ones and 3-ylidene indoles.