Abstract: A method of manufacturing an optical fiber having no defect in the refraction index profile comprising manufacturing a bare fiber by heating and extending a core starting material and forming a cladding layer on said core to produce a double-layer of the core and cladding with different refraction indices. Fine granules of oxide for the glass cladding can be formed by vapor deposition on the bare fiber, and these can be fused to form the cladding by heating. Another method for forming the cladding layer is to pass the bare fiber for the core through a fine hole provided at the bottom of a crucible in which the glass for the cladding is contained in liquid form.