Poly(trimethylene terephthalate) (M)/polypropylene (PP) blend nanocomposites were prepared by melt mixing of PTT, PP, and organically modified clay. The phase morphologies of the PTT/PP nanocomposites and the distribution of the clay in the nanocomposites were investigated using scanning electron microscopy, transmission electron microscopy (TEM), and wide angle X-ray diffraction. When PP is the dispersed phase, the domain size of the PP phase is decreased significantly with increasing the clay content from 0 to 5 wt%. In contrast, when PTT is the dispersed phase, the dimension of the PTT phase is a little larger in the presence of 2 wt% clay compared with the case of without clay. TEM observations indicate that the clay is mainly distributed at the phase interfaces along the phase borderlines. In addition, some intercalated clay tactoids (multilayer particles) are observed in the PTT matrix whereas no discernable clay particles can be found in the PP phase, indicating that the affinity of clay with PTT is higher than with PP. In the presence of 5 wt%. PP-graft-maleic anhydride, the phase morphology is much finer, and most clay is exfoliated and distributed at the phase interfaces forming phase borderlines in polygonal shape. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 3883-3890, 2009