Acid dissociation equilibrium constants for substituted 1,3-diphenyltriazenes were determined by means of spectrophotometric titrations. Measured acidity constants correspond to macroscopic equilibrium constants, since target substrates display prototropic tautomerism. Interestingly, experimental acidity constants for both symmetrically and unsymmetrically substituted 1,3-diphenyltriazenes obey a linear Hammett equation, implying that the Hammett reaction constants corresponding to substitution at the azo and amino phenyl sites are experimentally indistinguishable.