After vapor-grown carbon-fibers (VGCF) were added to resol-type phenolic resin, their influence on microstructure, thermal conductivity, flexural strength, and physical properties of the resin was characterized in this work. Resin with content 0-10 wt % VGCF was heat-treated at 230-2500 degrees C. As a result, it was observed that adding VGCF into resin during pyrolysis not only reduced weight loss but also limited shrinkage of resin. Moreover, adding VGCF to resin promoted the degree of arranging carbon basal planes and chemical densification of the structure of final heat-treated resins. At 2500 degrees C, the graphitized resin with 10 wt % VGCF enhanced flexural strength and thermal conductivity over 300%, while decreasing weight loss around 20% versus graphitized phenol-formaldehyde resin developed from the original resin. (c) 2006 Wiley Periodicals, Inc.