The influences of shape and size of powdered celluloses on the mechanical properties of polypropylene (PP)/powdered cellulose composites were investigated, comparing with talc and calcium carbonate (CaCO₃). The surface treatment of the fillers (cellulose and CaCO₃) with stearic acid prevented the fillers from aggregating. The interfaces of the PP/cellulose, the PP/talc and the PP/CaCO₃ were not adhered. For PP/cellulose composites, higher aspect ratio of cellulose caused the higher modulus than lower aspect ratio. Specific modulus of the PP/cellulose composites was slightly lower than PP/talc composites and higher than PP/CaCO₃ composites. Specific strength of the PP/cellulose composites was almost the same as that of the PP/talc composites and higher than that of the PP/CaCO₃ composites. From these results, PP/cellulose composites may be used as lightweight and high strength composites.