Carbon/carbon composites were prepared from PAN Base No-woven carbon fabrics, resol-type phenolic resin and Mesocarbon Microbeads (MCMBs), which is derived from coal tar. In this study, the effect on microstructure, flexural strength, electric conductivity and thermal conductivity of carbon/carbon composites with MCMBs contents ranging from 0 to 30 wt.% were examined during pyrolysis. The results showed that the carbon/carbon composite with addition of 10∼30 wt.% MCMBs has a higher density and preferred orientation than those of carbon/carbon composite without MCMBs during heat treatment. These composites also exhibited an improvement in flexural strength from 21.4% to 34.0%. These composites also showed an improvement in electric conductivity from 25.0% to 59.6% and that in thermal conductivity from 10.5% to 18.0%.