The present invention relates to a process for preparing optically active carbonyl compounds by asymmetrically hydrogenating .alpha.,.beta.-unsaturated carbonyl compounds in the presence of optically active transition metal catalysts which are soluble in the reaction mixture and have at least one carbon monoxide ligand. The present invention especially relates to a process for preparing optically active aldehydes or ketones, in particular citronellal, by asymmetrically hydrogenating the corresponding optically active .alpha.,.beta.-unsaturated aldehydes or ketones.