In this paper, an efficient synthesis of 3-spirooxindole 3H-indoles through the coupling and spirocyclization of N-aryl amidines with diazo oxindoles is presented. Mechanistically, the formation of the title products involves a cascade process including Rh(III)-catalyzed C(sp²)–H bond cleavage, Rh–carbene formation and migratory insertion, intramolecular nucleophilic addition and ammonia elimination. In general, this novel spirocyclization features easily accessible substrates with a broad scope and generality, redox neutral reaction conditions, formation of multiple bonds with high efficiency, and structurally and pharmaceutically attractive products.