The method of producing an alkali metal azide involves reaction of hydrazine with an alkyl nitrite in a solvent in the presence of an alkali metal hydroxide. As the solvent is used as aqueous solvent and the reaction ratio of hydrazine is controlled within the range between 50% and 90%. The method can produce with high purities and in high yields alkali metal azides useful as a raw material for the preparation of tetrazoles which can be used as an intermediate material for medicines, as a raw material for the preparation of organic azides useful for light sensitive materials for photo masks employed in the field of electronics industries, or as a major raw material for inflaters used in air bags for cars.