A spectral deconvolution method based on target factor analysis has been developed to determine pK(a) values of binary mixtures of monoprotic and/or diprotic ionizable compounds. The technique makes use of the approach of Frans and Harris, which has been implemented previously for mixtures of monoprotic compounds (Anal. Chem. 1985, 57, 1718-1721), to extract the unknown pK(a) values. The method has been illustrated by using the multiwavelength spectrophotometric titration data of binary mixtures of: 1. benzoic acid and phenol, 2. benzoic acid and nicotinic acid, 3. p- aminosalicylic acid and phthalic acid. It was demonstrated that the pK(a) values as determined in this study are in good agreement with the literature.