[en] Complex formation of Nb(V) with 7-phenylazo-8-hydroxyquinoline-5-sulphonic acid (Pazoxs) is described. Pazoxs forms a pinkish-orange water soluble complex with Nb(V). The stoichiometry of the complex is 1 : 2 (metal to ligand) as shown by moles ratio and Job's equimolar as well as nonequimolar continuous variation method. The complex shows maximum absorption at 480 nm. The most suitable pH range for complex formation was found to be 4.5-5.5. The present work was done at pH5.0 at 20+-1⁰C. Interference by various ions was studied and probable structures are suggested. Average value of the stability constant as found by Job's equimolar and non-equimolar and moles ratio method is 8.2 showing the complex to be sufficiently stable. Effect of time and temperature has also been studied. (author)