A series of 3-(1H-indol-3-yl)isoindolin-1-one derivatives were synthesized by the three-component reaction of a phthalaldehydic acid, primary amine, and 1H-indole in water under catalyst-free conditions. The reaction presented here has several advantages, such as clean, one-pot, and easy handling. The environmentally-friendly features make this procedure a sustainable method for the synthesis of 3-(1H-indol-3-yl)isoindolin-1-ones.