Synthesis of isonicotinic acid hydrazide (INAH) from citric acid was examined and its industrial application was perfected by the successful establishment of an advantageous process of preparing phosphoryl bromide and halogenation of citrazinic acid at an ordinary pressure (cf. Table II). Phosphoryl bromide was obtained in an 80% yield by the oxidation of phosphorus tribromide with potassium chlorate. Application of phosphoryl bromide to citrazinic acid, at ordinary pressure, yielded 2, 6-dibromoisonicotinic acid in a 70% yield.