Vapour-phase hydration of 1-butene at atmospheric pressure above 373 K shows similar features on both H-clinoptilolite and sulphonic acid ion-exchange resin : the initial reaction rate linearly increases with the partial pressure of 1-butene and passes through a maximum as a function of water pressure. Kinetics was evaluated accordingly. A decrease in the 1-butene isomerization rate indicated that under hydration conditions more than 99.9% of the acidic sites are hydrated. For the hydration, however, hydroxonium ions are the active centres where an adsorbed water molecule reacts with gas-phase 1-butene in the rate determining step. The equilibrated desorption of secondary butanol ends the reaction. The kinetic inhibition by butanol can be suppressed with water. Above ca. 0.2 bar water pressure inactive polydrated hydroxonium ions are formed.