Abstract--Noncrystalline aluminosilicates termed allophane and imogolite are common constituents of spodosols, soils derived from volcanic ash, and many inceptisols. The surface charge characteristics of their synthetic analogues may be used to better understand their ion retention properties. In this study, we determined the point of zero salt effect (PZSE) by potentiometric titration of allophanes with A1/Si ratios of 1.12, 1.52, and 2.04 and of imogolite with an A1/Si ratio of 2.02. We also used microelectrophoresis to determine the point of zero charge (PZC) at the particle shear plane for the same materials in C1 solutions of Li, Na, Cs, and tetramethyl ammonium. The PZSE decreased with decreasing A1/Si ratio for the allophanes, but the imogolite PZSE was much lower than that of the allophane with 2.04 A1/Si. The PZC was always higher than the PZSE of the same material, especially for imogolite. The results are best explained if cations reside within the hollow tubes ofimogolite. This conclusion is supported by a fluorescence study that showed that only quenchers smaller than the inner diameter of the imogolite tube could fully quench Ce-imogolite.