The size reduction and structural changes of talc induced by dry grinding with tumbling and planetary ball mills were investigated by means of particle size analysis, SEM observation, X-ray diffraction and TG-DTA. Size reduction of talc samples was observed to predominate in grinding using a moderate energy type tumbling ball mill. The resultant fine particles of ground talc were found to agglomerate with increasing grinding time. A morphological change of talc from the original platy shape to agglomerated spherical particles was clearly observed, although X-ray diffraction results show no intensive structural change within 684 ks grinding. In the case of energy-intensive dry grinding using a planetary mill, the talc changed its structure from a crystalline to an amorphous state. This change resulted in a decrease in density and an increase in strength of a single particle. The radial distribution function analysis of ground talc samples suggests the environmental change of magnesium from a parent octahedral to a tetrahedral coordination with increasing grinding time. A low temperature dehydroxylation reaction and a new exothermic peak at 1120 K for the ground talc samples were also detected in TG-DTA analysis. The variation in thermal behavior suggests a change in the hydroxyl component in the structure of ground talc samples.