Disclosed is a method of manufacturing an optical fiber perform using MCVD including dehydration and dechlorination, which executes the following process repeatedly with changing the composition of soot generation gas according to the refractive index profile, the process including the steps of: forming a soot layer having pores on an inner wall of a deposition tube at a temperature lower than the soot sintering temperature with putting soot generation gas and oxygen gas into the rotating deposition tube; removing hydroxyl groups with keeping the pores by putting dehydration gas into the deposition tube; removing chlorine impurities existing in the soot layer with keeping the pores by putting dehydration gas into the deposition tube; and sintering the soot layer by heating the deposition tube at a temperature over the soot sintering temperature.