The thermal conductivity of a semimetal Mg2Pb single crystal has been measured from 2 to 200 K. At low temperatures thermal conduction is by phonons limited by phonon scattering from the heavy hole Fermi surface. At higher temperatures the thermal conductivity contains both electronic and phonon contributions. A comparison of the thermal conductivity of Mg2Pb with the thermal conductivities of the related semiconductors, Mg2Si, Mg2Ge, and Mg2Sn, indicates that there is a significant bipolar contribution to the electronic thermal conductivity.