In the process of synthesizing alkylborazine compound represented by the chemical formula 2, by a reaction of a halogenated borazine compound represented by the chemical formula 1 with a Grignard reagent, thus synthesized alkylborazine compound is washed with water, or subjected to sublimation purification or distillation purification at least three times, and/or subjected to distillation purification at least twice. In the formulas, R1 independently represents alkyl group; R2 independently represents alkyl group; and X represents halogen atom.