Kinetic studies in aqueous solution on the replacement of the aqua ligands in cis‐[Cr(BigH)2(OH2)2]3+ (BigH = biguanide, C2H7N5) by 2,2′‐dipyridyl (dipy) and 1,10‐phenanthroline (phen) forming [Cr(BigH)2(AA)]3+ (AA = dipy or phen) have been made spectrophotometrically. In both the cases the reaction proceeds by a path purely first‐order with respect to the ligand. From the values of the rate constant at four different temperatures, values of the activation parameters, ΔH≠ and ΔS≠, have been evaluated for each system. The results are consistent with a mechanism involving outer‐sphere association of the reactants followed by transformation of the outer‐sphere complex in a dissociative process. Copyright © 1976 Verlag GmbH & Co. KGaA, Weinheim