PURPOSE: To synthesize the impurity-free fluoride glass.

CONSTITUTION: In the synthesis of the fluoride glass by the sol-gel method, a stage in which a wet gel obtained by oxidizing a precursor containing all cations constituting the fluoride glass is produced, the stage in which the gel is hydrolyzed by adding generally an acidic soln. and the stage in which the gel is dried are provided. Moreover, the stage in which the oxidized gel is treated with a fluorinating agent in a vapor phase at a temp. below the glass crystallization point is provided. This process more particularly makes it possible to produce a fluoride glass for optical fiber.