Abstract: Montmorillonite/Polyimide (MMT/PI) nanocomposite film was prepared with pyromellitic dianhydride (PMDA) and dimethylacetamide (DAPE) as monomers, and organic montmorillonite (MMT) treated by 16-decyltrimethyl ammonium chloride as inorganic reinforcement. The microphase of the PI/MMT film was characterized with TEM, XRD, TGA, DSC, etc. The results show that the proper content of 16-MMT in the matrix can lead to a nanophase reinforcement (1~2 nm in thickness) dispersion system. It is interesting thatthere was some orientation behavior in the matrix after 16-MMT was delaminated into sheets.