Novel 1.alpha.-hydroxy-24-dehydrovitamin D.sub.3 and its hydroxyl-protected derivatives; novel 1.alpha.-hydroxy-24-dehydroprevitamin D.sub.3 and its hydroxyl-protected derivatives; and novel 1.alpha.,3.beta.-dihydroxycholesta-5,7,24-triene or its hydroxyl-protected derivatives which are key intermediates for preparing the aforesaid compounds. Novel processes for preparing these compounds are also provided. 1.alpha.-Hydroxy-24-dehydrovitamin D.sub.3 has a pharmacological action of controlling the calcium metabolism of warm-blooded animals, and is useful as a prophylactic or therapeutic pharmaceutical for vitamin D deficient disease and related diseases.