Spectrophotometeric determination of cadmium (II), mercury (II) and manganese (II) is carried out with 1-(2 pyridylazo)-2-naphthol as complexing reagent in aqueous phase using non-ionic, surfactant Tween 80. The molar absorptivity, Sandell`s sensitivity, critical micelle concentration, 1-(2 pyridylazo)-2-naphthol, and metal ion concentration are studied. The method has been applied to the determination of these metal ions in municipal sewerage water and pharmaceutical samples.