The complex forming tendencies of some diphenols: 1,8-dihydroxynaphthalene-3,6-disulphonate (chromotropic acid: CTA: (H2L)(2-)] and 3,4-dihydroxybenzaldehyde (3,4-DHBAL: H2L) with scandium(III) were investigated in aqueous solution by potentiometry and spectroscopy. The measurements were carried out at 25.0 +/- 0.1 degrees C and at an ionic strength of 0.1mol.dm(-3) KCl. The stochiometric protonation constants of 3,4-DHBAL, CTA and the stochiometric formation constants of their Sc3+ ((aq)) complex species were determined. (ScL)(-) type binary complex of CTA is stronger than (ScL)(-) type binary complex of 3,4-DHBAL. The hydrolysis of CTA complexes resulted in [ScL(OH)](2-) and [ScL(OH)(2)](3-) type mixed hydroxo complexes, whereas Sc3+-3,4-DHBAL complex hydrolysis also occurs and the existence of only [ScL(OH)(2)](-) type is complex verified. Sc3+ ((aq)) can achieve coordination number seven in CTA complex while it is six in 3,4-DHBAL complex.