The acid dissociation constants of some 1 - (o - carboxyphenyl 3 ■ acetyl - 5 - aryl) for- mazans are determined in 40 % (v/ v) ethanolic buffer Solutions spectrophotometrically. The spectral changes with variation of pH were discussed in relation to the different ionic species existing in solution. The pKa values were discussed in terms of molecular structure and subs- tituent effect.