A method of fabricating an optical fiber doped with a rare earth component using a volatile complex, which flattens the light frequency response under a stimulated emission of radiation principle using a modified chemical vapor deposition method. Silicon tetrachloride (SiCl.sub.4) and oxygen are injected into a quartz reaction tube under a heating process, so that a cladding layer is repeatedly deposited. Then, a volatile organic metal chelate, silicon tetrachloride and oxygen are injected into the quartz reaction tube, and then heated and water-cooled to form a porous layer. At the same time, a rare earth element is deposited on the porous layer, to thereby form a core layer. Thereafter, via a high heating process, a preform is completed. Then, an optical fiber is obtained from the preform via a drawing-out process. Here, hydroxide ions (OH.sup.-) which occur as the organic ligand is volatilized and cause an optical loss of the optical fiber is removed as the porous layer is formed by the water-cooling, and an added rare earth content is easily controlled, so that the rare earth with high concentration is evenly distributed. Also, since the core laver adopts SiO.sub.2 and Al.sub.2 O.sub.3 as a host material instead of GeO.sub.2, the difference in a refractive index between the cladding and core layers becomes greater then 0.025, to thereby provide the optical fiber with excellent optical characteristics.