This work dealt with the effect of using an acrylic acid modified polypropylene (PP-g-AA) as a compatibilizing agent for the intercalation/exfoliation of an organically modified montmorillonite (o-MMT) in a polypropylene matrix (PP). Two PP-g-AA containing the same AA content (6 wt %) and having different molar masses were used. The o-MMT content was 0, 1, or 5 wt % of total mass and the PP-g-AA/o-MMT mass ratio was 0/1, 1/1, 2/1, or 5/1. Results of wide angle X-ray scattering (WAXS) and transmission electronic microscopy (TEM) showed that without the PP-g-AA, the o-MMT was dispersed in the PP/o-MMT in a micrometer scale, similar to a conventional microcomposite. With the PP-g-AA, the o-MMT was much better dispersed and its interlayers were intercalated and partly exfoliated by the polymer chains. Compared with the neat PP, some PP/PP-g-AA/o-MMT systems exhibited higher G' values and a yield stress at low frequencies, indicating that the PP-g-AA promoted the intercalation/exfoliation of the o-MMT. The compatibilizing efficiency of those two PP-g-AA was very similar. Generally speaking, the higher the PP-g-AA/oMMT mass ratio, the better the state of dispersion and the degree of intercalation/exfoliation. (C) 2008 Wiley Periodicals, Inc.