The hydrolysis of vinyl sulfides in acid solutions is shown to proceed via a mechanism analogous to that of vinyl ethers, with slow proton transfer to the carbon–carbon double bond to produce a sulfur stabilized carbonium ion. Relative rates of hydrolysis of compounds RXCH=CH2 are CH3S—, 41; CH3O—, 1500; C6H5S—, 1; and C6H5O—, 10.5. This order is compared with that of other systems which produce similar stabilized carbonium ions.