Three chromium(III) complexes of general formula [Cr(ox) 2 (pdaH)] 2-(where ox = C 2 O 4 2-and pdaH -is N,O-bonded 2,3-, 2,4-or 2,5-pyridinedicarboxylic acid anion) were obtained and characterized in solution. Acid-catalysed aquation of [Cr(ox) 2 (pdaH)] 2-gave two products: [Cr(ox)(pdaH)(H 2 O) 2 ] 0 (P 1 ) and cis-[Cr(ox) 2 (H 2 O) 2 ] 2-(P 2 ). The kinetics of these reactions were studied spectrophotometrically, within the 0.1-1.0 M HClO 4 range, and the pseudo-first-order rate constants for the oxalato (k obs1 ) and pdaH -(k obs2 ) ligands dissociation were calculated based on the determined pseudo-first-order rate constants (k obs ) and P 1 :P 2 molar ratio. The dependencies of the pseudo-first-order rate constants on [H ? ] are as follows: k obs1 = b 1 [H ? ] and k obs2 = b 2 [H ? ], where b 1 and b 2 are the second-order rate constants for the oxalato and pdaH -ligands dissociation, respectively. Kinetic parameters were determined and the mechanism of the pdaHligand dissociation is proposed.