In order to develop the cheap and efficient photocatalysts, kaolins were modified through calcination and acid leaching. In succession, the prepared samples were characterized using thermal gravimetric-differential thermal analysis (TG-DTA), scanning electron microscope (SEM) coupled with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-Vis) and BET specific surface area measurements (BET). Methyl orange, used as a model reactant, was degraded under UV light irradiation to evaluate the photocatalytic activities of the prepared samples. From UV-Vis spectroscopy analyses, an obvious increase in the red shift of the absorption edge was observed for the samples treated with acid. The acid sites generated during the modification of kaolin were determined through adsorbed pyridine analysis using infrared spectroscopy (Py-IR). Kaolins modified using over 30% H2SO4 contained both Brnsted and Lewis acid sites. Combining the results of photocatalytic experiment with the conclusions of Py-IR and XRD, the acid properties of the prepared samples were the main factors that affected their catalytic activity.