Chloroform-dioxane (1 : 1)-conc. HCl method was extended to the determination of epoxycarotenoids and total amount of β-carotene monoepoxides or diepoxides was determined photometrically by this method (absorbance was measured at 630mμ for monoepoxides and at 700mμ for diepoxides). Green substance derived from chloroform solution of β-carotene-5,6-monoepoxide and conc. HCl was treated with water to give the mixture of yellow-orange pigments. Column chromatography of this mixture over lime revealed the presence of 41 chromatograms (13 mains and 28 minors) and the structure of several main components were assigned as all-trans- or monocis- compound of retro-bisdehydromutatochromes (I), retro-dehydromutatochromes (II), dehydromutatochrome (III), mutatochrome (V) and (IV). Small amounts of cis-mutatochromes and keto-mutatochromes (?) were also detected. Reaction mechanism was discussed from spectral data.