A novel carbonylative addition of thiols (RSH) to terminal acetylenes (R′–CCH) takes place successfully in the presence of platinum catalysts under the pressure of carbonmonoxide, providing α,β-unsaturated thioesters (R′–C(C(O)SR)CH2) in good yields regioselectively. This ‘hydrothiocarbonylation’ reaction of acetylenes may include the formation of the platinum sulfide complex as key species.