In synthesis of hexaalkylborazine represented by the chemical formula 2 from a borazine compound represented by the chemical formula 1, a borazine compound represented by the chemical formula 1 is reacted with an alkene compound, in the presence of a catalyst. Wherein R1s may be the same or different and each R1 represents an alkyl group; and each R2 represents a hydrogen atom or an alkyl group, and at least one of R2s represents a hydrogen atom; and R3s may be the same or different and each R3 represents an alkyl group.