La1.6Ln0.4Zr2O7 (Ln= La, Nd, Dy, Er) nanocrystals were prepared by stearic acid combustion method. The samples were characterized by powder X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) nitrogen adsorption, transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The photocatalytic activity of La1.6Ln0.4Zr2O7 was evaluated by the photocatalytic degradation of methyl orange. The order of the photocatalytic activity was as following: La1.6Er0.4Zr2O7>La1.6Dy0.4Zr2O7> La1.6Nd0.4Zr2O7> La2Zr2O7. La1.6Dy0.4Zr2O7 showed that the best photocatalytic activity and the reason may be related to the big magnetic moment of Er3+. It may be considered largely to be caused by the partly occupied Ln4f levels. Since the solid samples have the same structure, the reason that La1.6Er0.4Zr2O7 shows the highest reactivity may be related to lowest Ln4f level of Er3+.