Using montmorillonite (MMT) and sodium carboxymethylcellulose (CMC) as raw materials, CMC/MMT nanocomposites were prepared by the solution intercalation technique. The microstructures of MMT before and after being intercalated were characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The results of XRD showed that when the adding amount of CMC increased from naught to 70wt%, the structures of MMT have no change basically; when the adding amount of CMC increased to 80wt%, the decrease of MMT (001) was significant; when the adding amount of CMC reached to 90wt%, the diffraction peak of (001) disappeared, which indicated that the layers of MMT have been exfoliated along (001) and the CMC/MMT intercalated structure has been obtained. The observations by HRTEM showed that the shapes of MMT are layer aggregation or agglomerated particles. The MMT added with 90wt% CMC has changed into intercalated structure with alternating MMT and CMC order mainly, and the intercalated structure was characterized at the atomic scale.