Abstract: In order to investigate the effects of preform structure on thermal conductivity of needle-punched quartz fiber/epoxy composites, the needle-punched quartz fiber/epoxy composites were prepared by needle-punching step by step and resin transfer molding process. The thermal conductivities of epoxy and needle-punched quartz fiber/epoxy composites with different preform structures were measured by using transient hot-wire method. Results show that the thermal conductivities of needle-punched quartz fiber/epoxy composites increase with the increase of fiber volume fraction. Compared with epoxy, the thermal conductivity of short-cut quartz fiber web reinforced epoxy increases by 35.9%. When hot-wire is parallel to the direction of fibers in the non-woven cloth of needle-punched quartz fiber/epoxy composites, the thermal conductivities of two needle-punched quartz fiber/epoxy composites, which are reinforced by short-cut quartz fiber web and non-woven quartz fiber cloth, increase by 45.5% and 46.4%, respectively. When hot-wire is perpendicular to the direction of fibers in non-woven cloth, the increase of thermal conductivities are 56.4% and 61.8%, respectively. The thermal conductivity of needle-punched quartz fiber/epoxy composites would be affected not only by the quartz fiber volume fraction, but also the volume fraction and orientation of the fiber in the non-woven cloth of preform.