A process for preparing an allylic sulfone of the following general formula (I), ##STR1## wherein, R is a hydrogen atom or a lower alkyl group, and containing both cis and trans isomers, by a reaction of a compound selected from the group consisting of geranyl chloride, neryl chloride, and linalyl chloride with a phenyl sulfinate of the following general formula (III), ##STR2## wherein, R is a hydrogen atom, or a lower alkyl group, and M is a sodium atom or potassium atom, in the presence of (i) tetralkylammonium iodide in an anhydrous condition or (ii) a zinc halide and an iodide.