The phase relation in the ZrO2-LaO1.5-MnOx system has been experimentally determined at 1200 degrees and 1400 degrees C in air and at 1200 degrees C in N-2 (P-O2 similar to 100 Pa). Tie lines between LaMnO3 and t-ZrO2 and between LaMnO3 and La2Zr2O7 are observed at 1200 degrees C in air. The geometry of the phase diagram changes at 1400 degrees C in air due to the appearance of a stabilized ZrO2 phase, found to be of cubic symmetry by backscattered electron diffraction. Tie lines of LaMnO3-c-ZrO2, LaMnO3-La2Zr2O7, and c-ZrO2-La2Zr2O7 are observed. At 1200 degrees C in N-2 (P-O2 similar to 100 Pa), the LaMnO3-t-ZrO2 tie line observed at 1200 degrees C in air is replaced by the La2Zr2O7-MnO tie line. Stabilization of c-ZrO2 is observed and a new compound forms, which is being reported for the first time. The proposed composition of the new compound is La2Zr5MnO14+delta.