X-ray tomography was used to reconstruct the microstructure of a carbon/carbon (C/C) composite to clearly reveal cracks and voids. The voids are divided into two categories (bubbles and micro-pores), and the cracks are classified into three categories (matrix, intra-bundle, and interfacial). The bubbles were found to account for 2–3% volume in the composite and intra-bundle porosity was in the range of 5–8%. The bubbles are spherical and intrabundle pores are cylindrical corresponding to structural model index (SMI). A three dimensional (3D) image of the network of cracks and voids was reconstructed for the better visualization. Interfacial cracks on a circular bundle/matrix interface were firstly segmented manually from the composite and special algorithms were used for segmentation and measurement of bundle/matrix interfacial a cracks of circular bundle in the composite. The crack thickness is obtained in the range of 0.012–0.018 mm and percentage debonding 20–50%.