A process for producing an optical fiber base extremely reduced in the content of impurities which deteriorate the transmission characteristics of an optical fiber. The process for producing an optical fiber base comprises dehydrating a base material obtained from a stack of fine glass particles and converting the base material to a transparent glass to produce a core member for an optical fiber base, stretching the core member so as to result in a desired core/clad proportion, and then adding a clad part thereto. The process includes: a step in which the base material is hung in a furnace tube having a heating zone and the base material is passed through the heating zone while moving it upward from a lower part to dehydrate the base material at a first temperature in a first atmosphere; and a step in which the base material is temporarily moved downward and is then passed through the heating zone while moving it again upward from a lower part at a second temperature in a second atmosphere to convert it into a transparent glass.