Four graphite powder fillers with different form and size were mixed with acrylonitrile butadiene rubber (NBR, acrylonitrile content at 26%) at 20,40 and 60 phr of the filler loadings, and the obtained compounds were characterized by SEM, tensile test, friction and wear test. Through the SEM observation, it was found that the expanded graphite could not be broken down to small particles uniformly when blended with rubber on the twin-roller. In the tensile test, the graphite with the smallest size possessed the best reinforcement ability as expected. The tribological properties of the rubber were improved when adding more graphite. The largest graphite particles imparted the lowest friction coefficient of the composites among four fillers, but the submicrometer graphite provided the best wear property to NBR. (c) 2006 Wiley Periodicals, Inc.