Energy content of marine sediment was measured by a bomb calorimeter. The optimal sample weight, the optimal combustion time and the optimal number of time for combustion were investigated. The mud samples (mud content 95%, ignition loss 12.8%) were collected in the center of Hiroshima Bay. Bomb calorimeters had the optimum range of 0.04g to 0.2g in sample weight and only unreliable values were obtained out of this range. A complete combustion of marine sediment sample took 7 minutes. Energy was completely radiated from a sediment sample, containing much minerals, by repeated combustion.