The average heat of thermal-neutron induced fission of U235 has been measured by a differential calorimeter. The average energy per fission observed by the calorimeter was 170.1 ± 1.2 Mev. On the basis of the thicknesses of the calorimeter materials and the theoretical energy loss equation, the β energy per fission observed by the calorimeter is 3.0 ± 1 Mev. and, on the same basis, the γ and neutron energy observed is negligible. The resulting 167.1 ± 1.6 Mev. for the average kinetic energy of the fission products is shown to be in good agreement with less direct determinations of this quantity.