An air-stable disilacyclopropene with a Si=C bond, 1,1,2-tris(tri-tert-butylsilyl)-3-(1-adamantyl)disilacyclopropene (2), was synthesized as yellow crystals by the reaction of ((t) Bu(3)si)(2)SiLi2 (1) with 1-adamantanecarbonyl chloride in THE The molecular structure of 2 was established by X-ray crystallography. The disilacyclopropene 2 represents the first CSi2 hybrid heavy analogue of cyclopropene featuring a skeletal Si=C double bond of 1.745(2) angstrom. The reaction of 2 with triphenylmethylium tetraarylborate in toluene produced 1,2-bis(tri-tert-butylsilyl)-3-(1-adamantyl)disilacyclopropenylium ion (3(+)), which was isolated in the form of the tetraarylborate salt as extremely air- and moisture-sensitive yellow crystals, representing the first isolable cyclopropenylium ion derivative with a silicon-carbon hybrid system.