Recently increasing attention has been focussed to heteroatcm-substituted cyclopropenyl cation system in order to eiucidate the features of the electronic behavior of this highly strained three-membered carbonium ions purturbed with hetero-atoms. l-3 Especially, trithiocyclopropenyl cations are of much interest, because hetero-[3]radialene structure (II) is expected to contribute to the ground state structure of I by the additional [2p-3d]r conjugation other than [2p-3p]rr conjugation of the carbon-sulfur bond of I. It has been reported I II III that such a [2p-3d]T conjugation was observed in a sulfur-containing carbonium ion, thiopyrylium ion. 4 3 If we assume that the three-membered ring (C3+ core) of I corresponds to a sp-carbon atom ss has been pointed out by us, 5 then we will get trithiocarbonium ion (III) which is already obtained by Tucker and Roof. 6 These consideration prompted us to synthesize trialkylthio-and triphenylthio-cyclopropenyl cations (I). The preparation of I also would arouse an attention from view point of preparative organic chemistry, because it could be a convenient synthetic intermediate as II is. We wish to report, in this comrmnication, the