An object of the present invention is to provide a process wherein 1,2,4-butanetriol can be obtained safely, easily and inexpensively without causing problems concerning wastewater. A malic diester, 3-hydroxy--butyrolactone or 3,4-dihydroxybutanoate represented by the following formulae (I), or a mixture thereof is reduced with sodium borohydride in an organic solvent to give 1,2,4-butanetriol represented by the following formula (II). When an optically active substance is used as the above-mentioned starting compound, substantially no recemization occurs during the reduction, and optically active 1,2,4-butanetriol is obtained. ##STR1##