A sensitive spectrophotometric method is developed for the determination of manganese in aqueous medium. The metal ion forms a yellowish brown coloured complex with resacetophenone oxime (RPO) in ammonium chloride and ammonium hydroxide buffer of pH 10.5. The 1:1 complex shows maximum absorbance at 380 nm with a Beer's law range of 0.09–1.7 ppm. The molar absorptivity and the Sandell sensitivity are found as 2.5 × 10 4 l.mole −1.cm −1 and 0.002 μg/cm 2, respectively. The stability constant of the complex calculated by Job's method is 7.5 × 10 5. The interfering effects of various cations and anions are studied. The present method is applied to the determination of manganese in some steel and alloy samples.