PROBLEM TO BE SOLVED: To solve the problem wherein a successive requirement to a new method for preparing an ultra-pure organometallic compound to be used for a CVD precursor is present.SOLUTION: The method of preparing an ultra-pure organometallic compound comprises using a microchannel device for synthesis in reacting a metal halide with an alkylating agent to produce the ultra-pure alkylmetal compound for processes such as chemical vapor deposition.