Compound oxides (NiFeO and CoFeO) were obtained by calcining layered double hydroxide (LDH) precursors prepared by microwave-hydrothermal method. The structure of LDHs and compound oxides was characterized by X-ray diffraction (XRD). The thermal behavior and flammability of polypropylene (PP) composites containing different types of compound oxides were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), and cone calorimeter. Fire performance characterization has demonstrated that both NiFeO and CoFeO can significantly increase the LOI of PP/IFR. NiFeO and CoFeO can improve the char quality of PP/intumescent flame retardant (IFR) composite and the thermal stability of formed char. The heat release rate (HRR) of a PP/IFR sample containing 2 wt % CoFeO could be decreased by 33%, compared with that of PP/IFR sample. The char residue of PP composites after cone test was characterized by laser Raman spectroscopy (LRS) and X-ray photoelectron spectroscopy (XPS). It is suggested that compound oxides containing transition metals can enhance the flame retardancy of a PP composite through trapping free radicals in the gas phase and improving the char quality in the condensed phase.