The present invention relates to a process for enantioselectively preparing optically active 4-hydroxy-2,6,6-trimethylcyclohex-2-en-1-one derivatives of the formulae (I) or (Ia) and to a process for preparing (3S,3'S)-astaxanthin of the formula (III), comprising the process for preparing the compound of the formula (I). ##STR00001##