Studies of the adsorption and desorption of H + ions and the adsorption of Cu 2 + ions on TiO 2 (anatase) were made by alkalimetric titration in 0.1 M (K)NO 3 solutions at 298.2 K using ion-selective electrodes and atomic absorption spectrometry. The adsorption is explained in terms of surface-complex formation. The active surface groups were defined as multifunctional sites consisting of bridged and terminal hydroxyl groups. With help of the computer program 'GRFIT,' a model for the sorption behavior was designed. The surface potentials were accounted for by the constant capacity approximation. The experimental results are explained by the general equilibria >S + p H + + qCu 2 + = >SH p Cu ( p + 2 q ) + q ; β S p - q , ( i n t ) = [>SH p Cu ( p + 2 q ) + q ][>S][H + ] p [Cu 2 + ] q e ( p + 2 q ) F ↓ / R T where >S denotes the neutral surface sites, and the stability constants log β S 1 , 0 , ( i n t ) = 5.40, log β S 1 , 0 , ( i n t ) = -7.75,log P;β S - 2 , 0 , ( i n t ) = -17.21, log β S 0 , 1 , ( i n t ) = 4.76,log β S - 1 , 1 , ( i n t ) = -1.13, log β S - 2 , 1 , ( i n t ) = -6.74.