Hole-doped colossal magnetoresistance (CMR) materials La1-xAxMnO3 (A=alkaline metal, 0≤x≤1) has been extensively studied because of its colossal magnetoresistance (CMR) characteristic in a magnetic field. Recently, many suspicious electron-doped CMR materials have been reported. However, none of these ¡§pure phases¡¨ were supported directly by experiment evidences, instead, various impurity phases were found. The La0.7Ce0.3MnO3 (LCeMO) target forming by a solid state reaction method, after analyzing its crystal structure and electric transport properties, is also found to be decomposed into CeO2 impurity and a La deficient La1-dMnO3 phases. This is believed to because the doped Ce4+ ions transforming the Mn3+ ions to Mn2+ whose larger ionic radius (aMn2+ =0.83Å), comparing to that of Mn3+(0.645Å), makes the MnO6 structure instable. Therefore, instead of forming an instable phase, the sample prefers to decompose into different phases. In this study, we propose to grow LCeMO films on an in-plane-enlarged STO bottom layer which was grown under a tensile strain on MgO (c=4.216Å) substrate. We found that all as grown films exhibits insulating behavior. Nevertheless, the samples after a rapid thermal annealing process can easily decompose the films into multiphase.