Pulse radiolysis and quantum chemical methods were employed to study the oxidation of phenyl vinyl sulphide (PVS) and phenyl vinyl sulphoxide (PVSO) by   ^· OH and SO4^{· -} radicals. The ^· OH radical reacts by addition (k~ (1-2) x 10⁹ dm³ mol^-1 s^-1) and the PVS–OH (l_max = 310 nm) adduct was entirely converted into PVS^·+ (l_max = 310 and 550 nm) at pH 1. DFT calculations revealed that the vinylic OH adducts are in general more stable than the ring addition products and the odd electron spin in both radical cations is located over S and C atoms.