Abstract: 〖WT5HZ〗Abstract:〖WT〗A differential kinetic spectrophotometric method for simultaneous determination of Ru³⁺and ［RuNO³⁺ in the same system was developed. The initial apparent rate constant, reaction order in term of Ru³⁺or ［RuNO］³⁺ concentration, equilibrium constant for the reaction of bipyridyl and Ru³⁺or ［RuNO］³⁺ in the presence of hydroxylamine hydrogenchloride were determined. By measurement of the initial formation rate and the equilibrium concentration of the product Ru(bipy)²⁺₃ the concentrations of Ru³⁺ and ［RuNO］³⁺were easily calculated by solving the linear simultaneous equations. The recovery of Ru³⁺and ［RuNO］³⁺ is found to be 96％-105% and 95%-106%, respectively. The interference of several common metal ions is substantially eliminated by addition of EDTA as a masking agent.