The solid equal channel angular extrusion (ECAE) process on polypropylene (PP)/organic montmorillonite (OMMT) was carried out. Scanning electron microscopy, polarized optical microscopy, transmission electron microscopy, and X-ray diffraction were used to observe and characterize the samples structures. Experimental results show that both PP spherulites and OMMT particles were significantly deformed and orientated toward the shearing direction, and OMMT agglomeration particles were broken into needle-like primary particles, some even exfoliated into nanosilicate layers after twice ECAE processes due to the immense solid shear force. This solid process approach introduces a new way to prepare PP/OMMT nanocomposites. The mechanism of exfoliation between PP and OMMT was also discussed. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 2222-2227, 2012