Two synthetic and three natural magnetite samples that were obtained from an iron ore deposit located in Central-Western Mexico, were used to investigate the magnetite surface reactivity of different particle sizes towards aqueous Pb(II) and Zn(II).From these, the synthetic samples < 50 nm [specific surface area (SSA)] = 39.3 m 2 /g), < 5 mm (SSA = 7.3 m 2 /g), and natural samples 948-fine (SSA = 7.6 m 2 /g), 948 (SSA = 3.0 m 2 /g) and 996 (SSA = 1.4 m 2 /g), successfully removed Pb(II) from aqueous solutions at the investigated pH value of 5.8, but only the three first, finer magnetites removed significant aqueous Zn(II) at pH 7.0.The adsorption kinetics data were fitted using pseudo-second order and intraparticle models.The Pb(II) adsorption capacities were 140.1, 33.3, 65.4,69.8 and 17.0 mmol/g, for samples < 50 nm, < 5 mm, 948-fine, 948 and 996, respectively, while for Zn(II) they were 159.2, 38.8 and 28.2 mmol/g, for the first three previous samples, respectively.These adsorption capacities suggest that magnetite may play an important role as adsorbents of cationic contaminants in the environment, or that it may be used as efficient remediating agent, but it's limited to particle sizes with specific surface areas above 3 m 2 /g. Palabras clave: