The kinetic energy released in Chinese hamster splenctic cells for incident ultrasoft X rays with the energies from 0.9 to 1.55keV, which were from a laser-plasma X ray source, was calcualted by resorting to the energy spectrum integration method and the equivalent energy approach, respectively. In the calculations, the X ray transmission, attenuation, and energy transfer in the biological material were considered. A difference between the two calculations was found to be about 15%. The distribution of the kinetic energy relased in material (kerm) in the cells was also estimated using the chemical composition of the cells.