Abstract: The foamed wood flour-nano-montmorillonite (NMMT)/polypropylene (PP) composites were prepared by the batch foaming method using supercritical CO₂ microcellular foaming technology. Effects of NMMT on the microcellular structure and mechanical properties of the composites were explored by investigating crystallization behavior, rheological properties, cell morphology and compression properties. The results show that NMMT accelerates the crystallization rate of the PP matrix in the wood flour/PP composites, and reduces the crystallinity rate. This is beneficial to the formation of foamed homogeneous system and cell growth. The PP molecular chain is inhibited by the NMMT interlayer, resulting in the melt elasticity increasement of the wood flour/PP composites. The phenomena of cell coalescence and collapse are reduced, the average cell diameter of the foamed composites is decreased from 30.4 μm to 20.3 μm, and the uniformity of cell size is obviously improved. The compressive strength and modulus are increased by 187% and 223%, respectively.