A process for preparing dibenzylidene sorbitols or dibenzylidene xylitols by reacting sorbitol or xylitol with a substituted or unsubstituted benzaldehyde or alkyl acetal derivative thereof in the presence of an acid catalyst, a hydrophobic organic solvent and a water-soluble organic polar solvent, the process being characterized by using the hydrophobic organic solvent in an amount sufficient to permit the resulting dibenzylidene sorbitols or dibenzylidene xylitols to separate out as crystals and capable of maintaining the reaction system in the form of a gel to solid phase and by conducting the reaction with forced agitation.