The chemical behavior of natural todorokite in Th and U aqueous solutions with initial concentrations between 10 and 1000 mg L-1 and pH higher than the point of zero charge (pH(PZC)) of the mineral was investigated by instrumental neutron activation analysis and x-ray photoelectron spectroscopy. The experimental results indicated that considerable amounts of Th and U could be bound by todorokite through different sorption mechanisms (especially surface precipitation) depending on the pH. The maximum sorption ratios (R-d) reached 697 and 94 mL g(-1), respectively. Exploratory experiments using Pa-233 in 1-0.001 M HCl solutions also indicated the ability of the material to interact with protactinium species even below its pH(PZC), exhibiting high R-d values (2.4-63.5 x 10(4) mL g(-1)). The precipitation of insoluble actinide hydrolysis products on the surface of the mineral can be attributed to the increase in pH due to simultaneous interaction with the H+ cations.