A method for producing an unsaturated vicinal diol compound represented by the formula (2): ##STR00001## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R are the same or different and each independently represent a hydrogen atom; a C1-C20 alkyl group which may be substituted with a halogen atom or atoms, a C1-C6 alkoxy group or groups, a C2-C7 alkoxycabonyl group or groups, a C6-C10 aryl group or groups, or a carboxyl group or groups; or a C6-C10 aryl group which may be substituted with a halogen atom or atoms, a C1-C6 alkoxy group or groups, a C6-C10 aryl group or groups, or a carboxyl group or groups; which comprises reacting an unsaturated epoxy compound represented by the formula (1): ##STR00002## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are the same as defined above, with water in the presence of a silicate containing at least one element selected from a group 5 element and a group 6 element of the long periodic table as a constituent.