Phase-pure lanthanum stannate (La2Sn2O7) nanoparticles with a pyrochlore structure were produced by a simple coprecipitation method for the first time. The optical properties of La2Sn2O7 synthesized by different conditions were investigated. They had different photoluminescence intensities around 400 nm at the same excitation wavelength. The size of La2Sn2O7 nanoparticles synthesized by the reverse-drop method was smaller than those synthesized by the nature-drop method. The nanoparticles became large rapidly with the dilution of the original reagent solution.