We determined the complete five-component transverse-isotropic-symmetry elastic-constant tensor for two graphite fibers: high-strength/low-modulus and low-strength/high-modulus. We did this in two steps. First, we measured ultrasonically the complete elastic constants of a metal matrix with embedded uniaxial graphite fibers. Second, we did an inverse—modeling calculation to extract the fiber’s elastic constants. This calculation requires three inputs: composite elastic constants, matrix elastic constants, and fiber-matrix phase geometry, principally the fiber volume fraction. We compare the results with those expected for a random quasiisotropic graphite aggregate and for a hypothetical graphite fiber with perfectly aligned basal planes.