A method of manufacturing an optical fiber base material being capable of dehydrating and sintering a porous glass base material without contaminating and damaging the porous glass base material and an apparatus of the same are provided. The method includes: forming a porous glass base material by depositing glass particles; providing a vessel which employs a composite tube, the composite tube including a synthetic quartz glass tube that is formed by melting a soot deposit formed by depositing glass particles which are produced by hydrolyzing silicide with oxyhydrogen flame, and a natural quartz glass tube that is formed by melting natural quartz with an electric furnace, the natural quartz glass tube jacketing the synthetic quartz glass tube; introducing dehydration reaction gas and inert gas into the vessel; heating the vessel which contains the dehydration reaction gas and the inert gas into the vessel; and inserting the porous glass base material into the heated vessel to dehydrate and sinter the porous glass base material.