To obtain an azo dye being useful for dyeing or printing a synthetic textile material, having good fastness, especially, thermal migration resistance by diazotizing a specified diazo component and coupling the product with a specified coupling component.

This dye is represented by formula I (wherein D is an aryl or hetaryl except 2,4-dinitro-6-ethanesulfonylphenyl; A is-CO-or-SO2-; B is an optionally substituted 1-4C alkyl; R2 and R2 are each independently a 1-4C alkyl optionally substituted with OH or a 1-4C alkyl; and R3 and R4 are each independently H or CH3, provided that A is SO2 when D is 6- nitrobenzothiazolyl). The dye is obtained by diazotizing a diazo component represented by the formula: D-NH2 (wherein D is as defined in formula I) and coupling the product with a coupling component represented by formula II (wherein A, B, R1, R2, R3, and R4 are each as defined in formula I).