In this experiment, seedlings of rye, maize and wheat were exposed to gamma rays with the doses of 77.2 Gy, 144.75 Gy and 289.5 Gy and a dose rate of 1.42 Gy/min. Root tips were taken for electron microscopic studies. The results indicated: As the increase of exposures and elongation of time after exposure, the degree of vacuolation in the root tip cells were increased up to intense vacuolation. The endoplasmic reticulum swelled gradually. Band-like and reticular vacuoles were formed from swelled endoplasmic reticulum. Endoplasmic reticulum and golgi apparatus were responsible for the vacuolization of the cells. Nucleus changed there shapes irregularly and sometimes micronucleus or micronuclei could be observed. Mitocondria cristae decreased, even disappeared, the matrix turned to light and outer and inner membrane broke forming disabied structures. No obvious structure damages were found on the golgi apparatus and cell wall.