PURPOSE: To provide a process for production of the optical fiber soot capable of stabilizing the refractive index distribution of the optical fiber soot and efficiently adjusting a burner.

CONSTITUTION: Gaseous raw materials are introduced into oxyhydrogen flames 4 formed by the burner 3 installed in a reaction vessel 1 and glass particulates are synthesized by a flame hydrolysis reaction, etc. The glass particulates are deposited on a seed rod 2 inserted into the reaction vessel 1, by which the optical fiber soot 5 is produced. The vapor phase chemical species in the flames are excited by a laser beam 11C emitted from a dyestuff laser 9 and the fluorescence emitted by the vapor phase chemical species is measured by a CCD camera 15, by which the spatial distribution of the vapor phase chemical species is measured. The conditions in the reaction vessel 1 are controlled by the result of the measurement.