Longitudinal and transverse ultrasonic velocity measurements were made to obtain elastic moduli of ceramic compacts and continuous fiber ceramic composites (CMCC) as a function of porosity volume fraction. The ceramic compacts were hot pressed silicon carbide and the CMCC were Nicalon fiber reinforced silicon carbide, manufactured using a forced chemical vapor infiltration (FCVI) process developed at Oak Ridge National Laboratory [1]. The purpose of the SiC powder compact study was to obtain experimental results of elastic moduli for various porosity level and to compare the measured results with predictions based on theoretical models. For chemical vapor infiltrated Nicalon/SiC ceramic composites, elastic constants data at different porosity level were not readily available in the literature. The purpose of the study was therefore to generate a more complete set of modulus data as a function of void content. These results can be used for the optimization of the manufacturing process and for comparison with mechanical testing results.