Abstract: Various ionizing radiations transfer their energy to biological media by producing secondary electrons. In the diagnosis and therapy of nuclear medicine and BNCT, the radionuclides distribute heterogeneously at cellular scale. In order to understand the interaction between ionizing radiation and biological medium, the study of cellular microdosimetry for electrons is needed. S value and the single event specific energy distribution are simulated by several codes, which include different Monte-Carlo methods. The result for S value is in agreement basically with the result of the MIRD committee and other simulations. The singleevent specific energy distribution in cell is agreed well with the result of the PENELOPE code.