There are disclosed novel derivatives of 26,26,26,27,27,27-hexafluorovitamin D.sub.3 having fluorine atom at the 23- and/or 24-position which have an excellent pharmacological activity and a process for production thereof. The novel compounds are represented by the general formula: ##STR1## wherein R.sub.1 ' denotes a hydrogen atom, a hydroxyl group or a protected hydroxyl group, R.sub.2 denotes a hydrogen atom or a protecting group for hydroxyl group, R.sub.3 denotes a hydrogen atom, a fluorine atom, a hydroxyl group or a protected hydroxyl group and R.sub.4 and R.sub.4 ' each denotes a hydrogen atom, or one of them denotes a hydrogen atom and the other denotes a fluorine atom, hydroxyl group or a protected hydroxyl group or R.sub.4 and R.sub.4 ' are combined to denote an oxo group, with a proviso that at least one of R.sub.3, R.sub.4 and R.sub.4 ' denote a fluorine atom. The process for production thereof comprises subjecting to thermal isomerization a compound represented by the general formula: ##STR2## wherein R.sub.1 ', R.sub.2, R.sub.3, R.sub.4 and R.sub.4 ' are the same as defined above, to thermal isomerization and optionally further to deprotection reaction.