PROBLEM TO BE SOLVED: To provide a method of a glass preform for optical fibers which has reduced variation of optical characteristics, a glass preform for optical fibers, an optical fiber and method of calculating optical characteristics of an optical fiber.SOLUTION: Provided is a method of producing a glass preform for optical fibers which comprise: a core part 2 composed of pure silica; a depressed part 3 having a refractive index which is smaller than the refractive index of the core part 2 and decreases from the inner peripheral side toward the outer peripheral side; and a jacket part 4 which has a refractive index smaller than that of the core part and larger than the refractive index of the depressed part 3. Taking the difference between relative index differences of the innermost periphery and the outermost periphery of the depressed part 3 as &Dgr;P and the difference between relative index refractive index differences of the innermost peripheries of the jacket part and the depressed part 3 as &Dgr;G
