The effect of alkyl chain length of chelating reagents on the complexation kinetics of 8-quinolinol (HQ) and 5-alkyloxymethyl-8-quinolinol (HC(n)Q; n = 1, 2, 3, 5, 8) with transition metal ions(M2+ : Ni2+, Zn2+) at liquid-liquid interfaces is studied by dynamic interfacial tensiometry. A decrease in the dynamic interfacial tension is caused by the interfacial adsorption of a 1:1 complex (M(C(n)Q)(+)) The interfacial complexation kinetics for Zn2+ is controlled by the diffusion of ligands from the bulk organic phase to the interface. For Ni2+, the kinetics is also diffusion-controlled for the ligands with short alkyl chains; however, it is controlled by the complexation reaction at the interface for those having longer alkyl chains. The interfacial complexation rate is found to be faster for Zn2+ than for Ni2+, and it correlates closely with the partition coefficient of the ligands. For the reaction-controlled complexation kinetics, a new procedure for calculating the interfacial complexation rate constant (k(1)) is proposed, and hi values for the reaction with Ni2+ at the heptane-water interface are calculated as 1.7 x 10(-5) m s(-1) M-1 (1M = 1 mol dm(-3)) for HC(5)Q and 2.2 x 10(-5) m s(-1) M-1 for HC(8)Q.