Abstract: Voids produced in the manufacturing process have significant influence on the mechanical properties and failure modes of carbon fiber reinforced epoxy resin (CF/EP) composite, which highly desire an accurate nondestructive evaluation of the void content and a reliable prediction of compressive properties based on the measured void content. In this paper, the effects of voids on ultrasonic attenuation coefficient and compressive properties were investigated extensively. CF/EP composite laminates were fabricated of quasi-isotropic layups and produced by applying various autoclave pressures of 0.7-0.2 MPa and increasing prepreg out storage time of 30-180 days to acquire controlled levels of void content. The void content, ranged from 0% to 3.0%, as well as the microstructure of intra- and inter-laminate voids could be verified and characterized using light microscopy. Ultrasonic reflection test was performed on laminates containing voids and the correlation between ultrasonic attenuation and void content, namely α_v=1.08P_v²(P_v is void content), was established theoretically and experimentally, which gave good duple-path agreement with published experimental results of ultrasonic through-transmission test, namely α_v=0.61P_v². Then, the dependency of the reduced compressive strength on laminates containing voids was investigated experimentally by counter-posing the compressive performances of four types of CF/EP composite laminate specimens, namely 0° un-tabbed, 90° un-tabbed, 0° tabbed and 90° tabbed. The result shows that the compressive strength of CF/EP composite laminates significantly decreases with the increasing of void content, saying a drop of 13.7% with void content up to 2.5%.The microscopic examination of the compressive failure modes shows that the microstructure of voids of CF/EP composite laminates also has a significant effect on the compressive failure mode, which can be attributed to the initiation and propagation of micro cracks, the reduced fiber-matrix bonding as well as the micro-buckling of fibers.