A water-soluble iron porphyrin, a meso-tetrakis(l-methyl-4-pyridyl)porphinatoiron(III) complex (FeTMPyPX5; X=OCH3 or halide), was successfully applied as a catalyst of indamine dye formation, which can be used for the determination of hydrogen peroxide in an acidic media. The dye formation process includes an oxidative coupling of N,N-dimethylaniline and 3-methyl-2-benzothiazolinone hydrazone with hydrogen peroxide. The absorbance of the formed dye was measured at 590 nm with a spectrophotometer. The materials were stable and the reaction was specific for hydrogen peroxide without any influence of molecular oxygen at low pH, 1–2. The method showed easy handling in the concentration range of (0.3 ~3.7)×10−5 mol dm−3 with a correlation factor: 0.9998 and RSD=1.74%. This method can be used for the determination of hydrogen peroxide generated through enzymatic processes.