To provide a method for manufacturing an optical fiber perform capable of manufacturing the optical fiber perform in which OH groups are sufficiently removed without degradation in production efficiency, and a method for determining dehydration conditions of a porous glass perform.

The method includes a dehydration process of dehydrating the porous glass perform having a porous glass layer by making the perform pass through a heating area in a dehydrating gas atmosphere. The dehydration process is performed by setting Pcl so as to satisfy 0.0773xe7.4873x≤PclxTxL/V according to ρ, T, L when the gaseous chlorine partial pressure in the dehydrating glass is defined as Pcl (Mpa), the treatment temperature as T(°C), the length of the region of ≥1,150°C in the temperature in the heating region as L (mm), the relative moving speed with respect to the heating region of the porous glass perform as V(mm/h), and the average bulk density of the porous glass layer as ρ(g/cm3).

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