BALB/c mice and human intestinal epithelial cells were irradiated to different doses by 60Co γ-rays. They were sampled for chromosome pattern analysis, intestinal morphology, and a number of other biomedical tests to investigate mechanisms of acute intestine injury by γ-ray irradiation and its effective treatment methods. The resuits indicated that:( a ) The intestinal epithelium stem cells from the normal mice (including infantility crypt cells ) could survive at intestinal crypt in mice after irradiation.(b) Bell-shaped curves correlating the crypt survival fraction and exogenous nucleic acids (RNA, DNA)doses were obtained, with the optimal doses for different routes of administration estimated.( c ) Comparing the different routes ( regional intestinal lumen, intramuscular, hypodermic, intraperitoneal and intravenous ) of RNA (ribonucleic acid ) administration, the intravenous injection seemed to be the most effective.( d ) The earlier time of RNA administration, the more effective it was. One injection within 6h after irradiation had the same effect as multi-injections.( e ) The intestinal RNA could enhance the crypt survival of all small intestines segmentes in mice after γ-irradiation, increase the number of leucocytes and platelets in the peripheral blood and enhance the formation ability of bone marrow GM-CFU in mice after γ-irradiation.(f) The intestinal RNA could decrease apoptosis and inhibit the expression of P53 in intestinal crypt cell after γ-irradiation.( g ) The intestinal RNA may improve the cell survival by regulating the cell cycle of the irradiated cells.( h ) The change in the gene expression of the irradiated small intestinal tissue could be induced by the intestinal RNA administration, and 18 new gene sequences or fragments which were related with damage recovery of the intestine RNA administration (the registration number was AF240164-240181 in GeneBank) were found.This fact suggests that: (1) Intestine epithelium stem cell of normal mice, including infantile crypt cells, may survive at crypt in mice after irradiation. (2) Exogenous RNA may help recovery of the intestine injury after γ-ray irradiation, and intestine RNA may increase the crypt survival and facilitate damage recovery of hemopoiesis and intestine tissue by gene regulation, changing cell cycle, decreasing apoptosis, and promoting the recovery of damage cells.