A multi-coupling type acid dye, C.I Acid Brown 75, consists of one coupling component) resorcinol which has several coupling positions, and three diazo components ; H-acid, picramic acid(PRA), and pnitroaniline(PNA). Since the reactivity of each coupling position of resorcinol and diazonium salts is different, color characteristics and yield of the dye are greatly assisted by the coupling order and conditions. In this study, the diazotization methods and stability of diazonium salts were investigated and discussed for the basic data needed in the synthesis of the dye. H-acid was diazotized by the reverse methods picramic acid by the disperse method, and pnitroaniline by the catalytic method with high yield. Diazonium salts were irlatively stable in acidic conditions, but these showed different stability in coupling conditions. The order of stability of diazonium salts in aqueous solution was PNA< PRA< H-acid.