A study has been made of the kinetics of hydration of unsaturated C-8 and C-12 alicyclic epoxides (5,6-epoxy-cis-cyclo-octene and 9,10-epoxy-1,5-cis,trans-cyclododecadiene) in a heterophase liquid-liquid system with the use of hydrocarbon solvents. It has been established that the reactivity of the epoxy group during hydration is determined by features of the conformational structure of the initial molecule. On the basis of the data obtained, conditions are proposed which ensure the almost complete conversion of the epoxide into the target 1,2-diol when the process is carried out in the presence of catalysts of the acid type.