Abstract: The fire retarded synergistic agents of montmorillonoite (MMT), zinc borate (ZB) and MnO₂ were respectively blended with the intumescent fire retardant (IFR) to prepare the fire retarded korean pine wood flour/polypropylene composites. The fire retarded synergistic effect was evaluated by the thermal analysis of TG, DTG and DSC and was further validated by FTIR and SEM. The results indicate that there is some fire retardant synergy among the three kinds of synergistic agents and IFR. MMT decreases the heat release and increases the char residue significantly. The synergistic effect of ZB is mainly incarnated in the second stage of thermal decomposition, and it can result in the foamed char residue. While the role of MnO₂ is in the first stage of thermal decomposition, and it promotes the decomposition of ammonium polyphosphate(APP) in advance, reduces the pyrolysis rate of the system, and makes the char residue more stable and dense.