In a heat fixing member which is a seamless type cylindrical heat fixing member having an elastic layer, the elastic layer is mixed with carbon fibers, and the elastic layer has a thermal conductivity of 1.0 W/(mK) or more in the thickness direction thereof. A heat fixing member is provided which is more improved in the thermal conductivity in the thickness direction, can efficiently supply heat to the heating object (recording medium) at the time of high-speed printing, can give fixed images having a high glossiness in virtue of the elastic layer, which has secured a sufficient flexibility. A high-performance heat fixing assembly is also provided which can conduct sufficient heat to toner images even if the dwell time is shortened.