Crystals comprising (2R)-2-propyloctoic acid and an amine which retain the pharmacological effect of (2R)-2-propyloctoic acid and can be safely used as a medicinal raw drug for peroral solid preparations. Of these crystals, the crystals especially with dibenzylamine are advantageous because not only the crystals themselves are useful as a medicinal raw drug but also use of the crystals as an intermediate can yield (2R)-2-propyloctoic acid having an optical purity exceeding 99.5% e.e., which has not been obtained hitherto.