To obtain the subject compound in high yield by with column chromatography from a mixture of dehydrocholesterol and/or lumisterol and/or tachysterol and other component(s).

The subject compound is obtained according to the following procedure: a mother liquor consisting of a mixture of dehydrocholesterol and/or lumisterol and/or tachysterol and other component(s) is first subjected to thermal isomerization followed by column chromatography using, as a mobile phase, supercritical or liquid carbon dioxide pref. spiked with a polar modifier, with modified silica gel as a stationary phase as desired, to effect removing the remaining 7-dehydrocholesterol and tachysterol, and the resulting effluent is recycled to an irradiation batch; the objective vitamin D3 can be crystallized from the useful fraction thus afforded and the vitamin D3, the other objective previtamin D3 and lumisterol left in the resultant solution are similarly recycled to the irradiation batch.