In situ elastic properties of the fiber and matrix in composites obtained via chemical vapor infiltration/chemical vapor deposition (CVI-CVD) have been determined using acoustic microscopy. An unusually high frequency was used to attain the resolution that was required by the structure and small size of the constituents in these nonhomogeneous materials. A coupling liquid was prepared with acoustic properties that were chosen with consideration of the high frequency and the material characteristics. Local measurements on the fibers and matrix were achieved by studying the acoustic signature that was processed on very small areas. The elastic modulus of the fibers and matrices was deduced from the velocity measurements.