An investigation has been made of the dihydroxylation of 4-vinylcyclohexene, individual methylcyclohexenes and a mixture of 1,3-dimethylcyclohexane isomers. It has been established that the most effective catalyst is a complex produced by the reaction of molybdenum oxybromide, acetic acid and hydrogen peroxide. The yield of corresponding diols in the presence of this complex is 46-83.3%, with a process selectivity of 70.0-90.7%. The dependence of the direction of oxidation of cyclo-olefinic hydrocarbons on the nature and concentration of the organic acids used has been determined.