Short 13 x 700- mu m C fibers and mesocarbon microbeads oxidized 3 hrs./80 degrees C and 24 hrs./room temp. with conc. HNO3 and dried, were added, 0.5 and 1%, to cement mortars. The hot-oxidized C was superior as a modifier of cement-C composites. Spherical C raised the bending and the compression strengths and the oxidized C fibers (1%) enhanced the bending strength. Nonmodified C (0.5%) increased the shrinkage of the composites.