PURPOSE: To obtain industrially and advantageously the titled compound in high purity, by the presence of a very small amount of a magnesium alkoxide in the reaction system in reacting metallic magnesium with an alcohol using the metallic magnesium having a specific particle diameter.

CONSTITUTION: Metallic magnesium is reacted with an alcohol, preferably a monovalent 1W4C saturated alcohol to produce a magnesium dialkoxide. In the process, metallic magnesium having 50W500μm, preferably 200W450μm average particle diameter is used as the metallic magnesium, and ≥0.05wt%, preferably 0.1W1.0wt%, based on the alcohol, magnesium dialkoxide, preferably granular form having 300W1,000μm average grain diameter is present in the reaction system.