An easy, rapid and sensitive novel spectrophotometric method for estimation of trace amounts of Promethazine-HCl in aqueous solution is described. The method is based on using the oxidative coupling reaction of Promethazine-HCl with m-amino benzoic acid reagent at pH1.2 in the presence of N-bromosuccinimide to produce an intense green color, water soluble, product which exhibit maximum absorbance at 592 nm. Beer's law is obeyed over concentration range of (2-26 µg/ml), with a Ԑ 9.754×〖10〗^3 l/mol.cm, Coefficient determination (R2=0.9991). Sandell̕s index of 0.03289 µg/cm^2, the average recovery is 100.396 %, RSD does not exceed 0.3096 %, LOD of 0.1949 µg/m1 and LOQ of 0.5905 µg/m1. The proposed method was applied successfully for determination of PMZH in its pharmaceutical formulations..