Porous χ-Al2O3 is a new material for fabricating coated inkjet printing paper. Paper coated with χ-Al2O3 powders has excellent water fastness. This study investigated the dye-fixing ability of χ-Al2O3 powders through measurements of adsorption isotherms. The variations in zeta potential, pore volume, pore size distribution, and specific surface area of χ-Al2O3 powders during the dye-fixing process were also examined. The results show that χ-Al2O3 powders have a strong affinity to dye colorants. The adsorption isotherm is classified as HA-type and the adsorption data fit the Langmuir model. In addition to the positive-charged surface of χ-Al2O3 provides cationic sites for fixing dye colorants via electrostatic interaction, the porous structure on the surface of χ-Al2O3 particles plays an indispensable role in trapping the colorant.