The phase relations in the ZrO2-CeO2-La2O3 ternary system at 1500 degrees C were studied by X-ray diffraction (XRD), petrography, and scanning electron microscopy in the overall concentration range. The samples of different compositions have been prepared from nitrate acid solutions by evaporation, drying, and calcinations at 1100 degrees and 1500 degrees C. The solid solutions based on various polymorphous forms of constituent phases and ordered phase of La2Zr2O7 were revealed in the system. No new phases were found. The isothermal section of the phase diagram for the ZrO2-CeO2-La2O3 system has been developed. It was established that in the ternary ZrO2-CeO2-La2O3 system there exist fields of solid solutions based on hexagonal (A) modification of La2O3, monoclinic (M), and tetragonal (T) crystal modifications of ZrO2, cubic modification of CeO2 with fluorite-type structure (F), as well as pyrochlore type ordered phase of cubic symmetry La2Zr2O7 (Py). The refined lattice parameters of the unit cells for solid solutions and microstructures of the definite field of compositions for the systems were determined.