A new colour reaction of iron(III) with 5-Br-DMPAP has been studied systematically. In dilute acetic acid solution (0.06–0.8 N), iron(III) can form a coloured complex with the above-mentioned reagent.The complex exhibits maximum absorption at 600nm, and the value of the apparent molar absorption coefficient is found to be 7.6 × 104. The composition of the complex is also established as Fe(III): 5-Br-DMPAP = 1:2 by the methods of continuous variation and mole ratio, as well as slope ratio. The Lambert-Beer law is obeyed in the range of 0 to 0.8μg iron/ml.