Ruthenium-catalyzed [2 + 2 + 2] cocyclization of diene-yne was developed. The reaction conditions were very mild; that is, a toluene solution of diene-yne was stirred in the presence of 5 mol % of Cp*Ru(cod)Cl. Tricyclic carbo- or heterocycles were obtained in high yields from corresponding straight carbon-chain compounds.