Carbon foams are used as insulation materials at high temperature. The carbon foams are fabricated by pyrolyzing thermosetting resin derived from polymer foams. Phenolic resins are a good source of carbon/carbon composite materials due to low level of toxic gas emission and high heat resistance. However, the carbon foam based on the phenolic foam has low mechanical properties because pyrolysis of neat phenolic resins can lead to glassy carbon. In the previous study, mechanical properties of the carbon foam were improved by reinforcing the nano-particles in the precursor. Because the phenolic foam reinforced with nano-particle has high cell density and cell uniformity that affected at the properties of carbon foam. However, it has low reinforcement effect of nano-particles by aggregation of particle. In this study, polyacrylonitrile (PAN) which has high thermal stability, high mechanical properties, and high carbon yield by intermolecular cyclization after carbonization process was reinforced to improve the mechanical properties. The phenolic foams reinforced with PAN precursor were fabricated by using microwave and were carbonized using a furnace. The cyclization index and crystal phase of carbon foam were observed with X-ray diffraction (XRD) and Field emission scanning electron microscope (FE-SEM) images. The physical properties of carbon foams reinforced with PAN precursor were characterized by measuring compressive strength and thermal conductivity. And thermal stability was estimated by using thermo gravimetric analyzer (TGA).