The indoloquinazolinone ring system has attracted considerable attention as a pharmacophore, because it shows various biological activities. The reported synthetic methods for the compound are simple and direct, but are not effective for the direct synthesis of indoloquinazolinone with a methylene group at the C-6 position. A palladium(0)-catalyzed cyclization of chloroquinazolinone via CH functionalization was developed for a concise synthesis of indoloquinazolinone derivatives. The presence of a substituent at the C-6 position is important for obtaining the product in good yield. The conformation of the reaction intermediate, in particular the NCPd bond angle, is important for the regioselectivity of the reaction.