Chlorinated olefins of general formula (I), ##STR1## wherein R is an alkyl, aralkyl, or alkenyl group substituted or not substituted by a lower acyloxy, lower alkyloxy, alkenyloxy or benzyloxy group, are prepared by the reaction of hypochlorous acid, generated by the reaction of sodium hypochlorite with a strong mineral acid, and olefins of general formula (II), ##STR2## wherein R is the same as defined above, in a two-phase system of water phase and organic solvent phase, not being miscible with water.