To purify the subject compound useful as a material for semiconductor industry, etc., by bringing a halide-containing alkoxysilane into contact with a metal alkoxylate under pressure, separating the alkoxysilane and removing the halide as an impurity simply and efficiently.

A halide-containing alkoxysilane (e.g. methyltrimethoxysilane) is brought into contact with a metal alkoxylate (e.g. sodium methylate) under pressure of 0.01-10kg/cm2 based on atmospheric pressure, treated at 90-150°C under stirring for 3.5 hours and distilled under normal pressure to separate the alkoxysilane. Consequently, a halide as an impurity in the alkoxysilane can be removed simply and efficiently. Further, since a small amount of the metal alcoholate is required, the number of treatments of the residue after the purification can be reduced to purify the objective alkoxysilane in excellent productivity.