Co(bpb) [bpbH2 is N,N'-o-phenylenebis(pyridine-2-carboxamide), C18H12N4O2] complex has active axial sites like a porphyrin complex. We studied the coordination of azide ion (N-3) to Co(bpb) in binary methanol-water mixtures by spectrophotometric method at the temperature range of 283-303 K. From the temperature dependence of the rate constant, activation parameters (Ea, △H#, △S#, and △G#) were obtained. An isokinetic temperature at about 302 K was observed at which the formation rate of Co(bpb)-N-3 was more or less independent of the solvent composition. The resulting △H against T△S plot showed a od linear correlation, indicating the existence of enthalpy-entropy compensation in azide complexation process. Under optimum conditions and based on the absorbance of Co(bpb)-N-3 produced through complex formation, a spectrophotometric method for the determination of N-3 in solution was developed.Alinear relationship between the absorbance and N-3 concentration was obtained in the range of (0.85-5.00)×10-4 mol·L-1 (3.6-21.0 μg·mL-1). The detection limit was 2.5×10-5 mol·L-1 (1.0 μg·mL-1). The proposed method was applied to the determination of N-3 anion in real water samples.