A highly sensitive catalytic quenching spectrofluorimetric method was described for the determination of V(V) based on its catalytic effect on the oxidation of 1,8-diaminonaphthalene by potassium bromate with Tiron as an activator in weakly acidicmediumandthereactionmechanismwasinvestigated.Thereactionwasfollowedspectrofluorimetricallybymeasuring the fluorescence intensity of 1,8-diaminonathphlene (DAN) (λex=356nm,λem=439nm)at a fixed time of 5min from initiation of the reaction. Under the optimum conditions, vanadium(V) can be determined in the range 0.05-50.0ng ml-1 with a S.D.=0.024 for 15 times measurements. The detection limit of the method was down to 0.0088ng ml-1 and the catalytic reaction activation energy was found to be 43.92kJmol-1. The proposed method was tested for the determination of vanadium(V)inriceandnaturalwatersamples.©2002 Elsevier Science B.V.Allrights reserved.