A method of manufacturing an optical fiber preform by passing a porous glass preform through a heating area in an atmosphere of dehydration gas to dehydrate the porous glass preform is provided. Values Pcl and V are set and dehydration is performed to satisfy 0.0773×e7.4873×ρ≦Pcl×T×L/V according to ρ, T, and L, where Pcl is a partial pressure of chlorine gas in the dehydration gas, T is a process temperature, L is a length of an area in the heating area where a temperature is 1150° C. or higher, V is a relative moving speed of the porous glass preform with respect to the heating area, and ρ is an average bulk density of a porous glass layer.