A process for producing powders of metal compound containing oxygen including the steps of: feeding at least one material selected from a liquid material and a solution material obtained by dissolving solid ingredient in organic solvent via a liquid flow controller into a vaporizer; vaporizing the materials in the vaporizer; adding oxygen; heating; cooling; and crystallizing. Also disclosed is the product formed by this process, and apparatus used in performing the process. The process and the apparatus enable easily mass-producing fine powders of metal compound containing oxygen used as materials for optical crystals, nonlinear crystals or magneto-optical crystals with reasonable production cost.