The polymerization of styrene mechanochemically initiated by the grinding of talc was performed by using a vibrating ball mill. Talc used was one of layered clay minerals as well as montmorillonite. The effect of the grinding of talc on the polymerization of the styrene was investigated by characterizing the polymer formed and talc ground. The results revealed that of all the experiments we have performed thus far, styrene most abundantly polymerized by grinding of talc. The polymerization of styrene was closely related to the total surface area of the ground talc. The products obtained were the composites of talc particles and resulting polymer attached to the particle surface. From the analysis of the molecular weight distribution of the polymer, it was suggested that the polymerization of the styrene proceeded with two types of cationic active species which were produced by the grinding of layered clay minerals. Mechanochemical polymerization is expected to be one of the more promising production processes of polymeric nanocomposites when layered clay minerals can be ground to finer nanometer sized-particles.