Abstract: After rats being irradiated with 500 rads of 60Co γ-rays,on the 3rd,9th,15th and 30th day,we used improved Macgillivary (1972) and Fujitoni (1978) method to extract non-histone chromosemal proteins loose combining with DNA (UP) and non-histone chromosomal proteins tightly combning with DNA (UP) in chromatin.On the 3rd day after irradiation,rats liver UP decreased and on the 9th and 15th day UP increased,but it was higher than normal on the 30th day.The liver non-histone chromosomal proteins were isolated by improved O Farrell (1975) method,isoelectric focusing-SDS polyacrylamide gel electro-phoresis,using Coomassie Brilliant Blue R250 for staining.The protein spot products could be obtained with high reproducibility,100-150 protein spots could be seen in UP and 40-60 in NP.At different time after irradiation,the figure of electrophoresis,the range of molecular weight,the Ph gradient were similar to the control.The UP spots with high molecular weight diminished gradually.Spot A cleared up,and low molecular weight parts were increased.NP spots A,C,E darkened progressively,furthermore,new protein spot H appeared and gel plate had something to do with the development of radiation damage.The machanism of irradiation induced cancer and aberration etc.Have been discussed.It has provided an important molecular basis for radiation damage research.