Abstract: A highly sensitive colour reaction of niobium-4,5-dibromophenyl-fluorone(Br-PF)-CTAB-OP surfactants has been investigated spectro-photometrically. The complex of niobium(Ⅴ) is formed in 1.5-3.0N HCl medium. The apparent molar absorptivity is 2.1×10⁵ 1 · mol^-1 · cm^-1 at 540nm. The molar ratio of Nb(Ⅴ) : Br-PF in the complex has been estimated to be 1 : 2. Beer's law is obeyed for niobium in the range of 0-3μg/10ml.Al³⁺,Zn2+, Cd²⁺,Mn²⁺,CO²⁺,Cu²⁺,Pb²⁺ ,Fe³⁺ , Cr³⁺-large amounts, V(Ⅴ)170-fold, Cr(Ⅵ) 150-fold, Zr(Ⅳ), Mo(Ⅵ),La³⁺ , Th⁴⁺, Bi³⁺50-fold and W(Ⅵ)5-fold excess do not interfere with the determination of Nb(Ⅴ) (2μg/10ml), using EDTA, tartrate and +β-dithiocarbaminopro-pionic acid as masking agents.A simple and rapid method is successfully applied to the determination of small amounts of niobium in alloy steels without separating Nb(Ⅴ) from the accompanying elements.