Fluroxypyr is a widely used herbicide whose presence in natural waters has prompted research into its removal by adsorption. This article reports a kinetics study of fluroxypyr adsorption on a commercial activated carbon. The experimental study used a micro differential column batch reactor operated at three solution flow rates and two initial fluroxypyr concentrations, establishing a differential regime in order to obtain correct experimental data. Initial rates at zero coverage permitted the external transfer coefficient k(L) to be calculated. Internal surface diffusion coefficients D(S) were determined by using the Homogeneous Surface Diffusion Model running the FAST software and taking advantage of tabulated user-oriented solutions. This model satisfactorily fits the experimental data. DS values were 2.5 x 10(-14) and 4.2 x 10(-14) m(2) s(-1) for initial concentrations of 30 and 50 mg/L, respectively. These values were confirmed by experiments in a widely used shaken batch reactor with a determined kL value.