Visible light-activated photocatalyst calcium indate (CaIn2O4) has been successfully prepared by a new approach with lower temperature calcinations. The sub-micrometer-sized samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. High-purity CaIn2O4 particles were synthesized by controlling the sintering temperature and their photocatalytic performance were evaluated. Under visible light irradiation, 10 ppm of methylene blue solution was effectively degraded in 3.0 h. The excellent photocatalytic activity of CaIn2O4 is attributed to the high purity, small particle size, and large surface area because of lower sintering temperature by thermal decomposition of metal oxalate precursor.