Abstract: MMT-MDI was obtained by diphenylmethane-4,4'-diisocyanate (MDI) reacted with hydroxyl groups of the acidulated montmorillonite (MMT) surface, then caprolactam (CPL) was brought in to intercalate into the MMT-MDI layers and block on the excess isocyanate end groups, thereby the MMT-MDI-CPL was produced. Next, utilizing prepolymer solution intercalation method, the MMT-MDI layers and the MMT-MDI-CPL could be respectively intercalated by polyamic acid (PAA) in the solvent of dimethylacetamide (DMAC) to prepare the exfoliated nano-MMT/polyimide (PI) composite. Finally, the modified MMT and nano-MMT/PI composite were characterized by inductively coupled plasma optical emission spectrometry (ICP-OES), FTIR, TG, XRD and SEM. The results show that, MDI has been grafted on the hydroxyl groups of MMT surface. The interlayer spacing of MMT is expanded gradually by the modification of MDI, the intercalation and the block of CPL on MMT-MDI. And the XRD and SEM of nano-MMT/PI composite show that MMT in the PI matrix is fully exfoliated.