To determine the radiosensitivity and dose-survival characteristics of jejunal crypt cells, experimental study was done using total 40 mice. Single irradiation of 1,000 rad to 1,600rad was delivered to whole bodies of mice, using a cesium 137 animal irradiator. The number of regenerating crypts per jejunal circumference was counted, by using a jejunal crypt cell assay technique, and dose response curve was measured. The average number of jejunal crypt Per circumference in control group was $140pm10$. Mean lethal dose$(D_0)$ of moose jejunal crypt cell was 135rad.