Abstract: Two kinds of self-prepared montmorillonite (MMT) modified by poly (oxypropylene) amine hydrochlorides (POP) with large basal spacing, O-MMT1 and O-MMT2 (the basal spacing is 6.72 nm and 8.66 nm, respectively), were added into polypropylene-grafted-maleic anhydride (PP-g-MAH) or polypropylene (PP) by blending methods. The effects of blending methods, blending time, basal spacing of the POP modified MMT and PP-g-MAH on the microstructure of MMT/PP-g-MAH and MMT/PP composites were investigated. The results show that O-MMT1 with large basal spacing benefits the exfoliation of MMT in PP-g-MAH matrix during the solution blending and melt blending process. With the extension of blending time, O-MMT1 turns to the exfoliated state through transitional state from inserted layer type and MMT/PP-g-MAH composites with completely exfoliated state are obtained finally. A lot of MMT layers with "bilayer structure" are found at the transitional state in the solution blending process. In addition, the addition of O-MMT2 with larger basal spacing and PP-g-MAH, both facilitate the exfoliation of MMT in PP matrix so that the completely exfoliated nano-MMT/PP composites are obtained.