The thermal conductivity of single-walled carbon nanotube (SWCNT)/polystyrene composites, prepared by a method known to produce a uniform distribution of SWCNT bundles on the micrometer length scale, was measured in the temperature range from approximately 140 to 360 K. The thermal conductivity enhancement (50% for 1 mass % at 300 K) is reasonably constant above room temperature but is reduced at the lower temperatures. This result is consistent with the expected, large contribution of interfacial thermal resistance in SWCNT/polymer composites. Enhancements in electrical conductivity show that 1 mass % loading is in the region of the electrical percolation threshold.