Yttrium oxide doped polyaniline were successfully prepared through the In-situ polymerization reaction method to a different percentage of weight in the presence of oxidizing agent ammonium dichromate. The composite was analysed by XRD, FTIR, morphologic structure was considered by FESEM, whereas thermal equilibrium by TGA and DSC. The resultant of FTIR, XRD showed that the composition of composite has changed substantially by the addition of Y2O3, TGA-DSC analysis desirable that the thermal stability of yttrium oxide doped polyaniline was giant than that of polyaniline this indicates that the composites are gradually changing from amorphous state to crystalline state.