Apparatus and methods for making an optical fiber preform at low cost avoiding the apparatus from being damaged are provided. Apparatus for making an optical fiber preform by depositing glass particles on the circumferential surface of a glass rod comprises: a chamber, a plasma torch, a glass particle supplying part, a composition modification gas supplying part, and an exhaust part. The chamber surrounds the heating portion of the glass rod heated by the plasma torch. The plasma torch heats the glass particles by a plasma flame. The glass particle supplying part introduces glass particles towards the heating portion of the glass rod in the chamber. The composition modification gas supplying part introduces composition modification gas into the chamber in order to modify the composition of the glass particles to be deposited on the heating portion of the glass rod in the chamber.