To provide a method of protectively coating an optical fiber with a moisture-proof substance in order to temporarily protect the existing exposed part and a method of completely peeling the existing protective film if necessary, in the optical fiber wherein an optical fiber is exposed, the exposed part is heated and the only core diameter is enlarged.

Protective coating is applied by dipping the exposed part of the optical fiber into a solution of moisture-proof substance which is dissolved at a low temperature, hydrophobic, capable of preventing moisture absorbing and is easily dissolved in a volatile solvent and by immediately taking it out. The peeling method in characterized in that a clothe or the like is soaked with a very volatile solvent, the bare part of the fiber is put on from the upper side, held between, dissolved by the solvent and thereafter, physically wiped off.