PURPOSE: To produce a stable solution, by adding monoethanolamine, diethanolamine or triethanolamine to a methyl alcohol solution of an aluminum halide and carrying out methoxidation reaction.

CONSTITUTION: A methyl alcohol solution of an aluminum halide is added with one or more amines selected from monoethanolamine, diethanolamine and triethanolamine (the molar ratio of aluminum halide to amine is preferably 1 to 0.5W3) to effect methoxidation reaction and the product is preferably treated with an ion-exchange resin to obtain a stable aluminum methoxide solution having remarkably improved purity. When the aluminum methoxide solution is hydrolyzed with water, fine powder having extremely high purity can be produced. The powder is useful in the field of ceramics, etc.