The article is dedicated to the problem of increase of viability of castor-oil plant seeds under the conditions of their ex situ conservation with the help of millimeter radiation (MMR). Various parameters of seeds and seedlings were determined: physiological (germinating power and germinability of seeds, rate of growth of seedlings), biochemical (enzymatic activity and protein synthesis in seedling rootlets) and genetic (number and range of chromosome aberrations). It was revealed that influence of millimeter radiation with the wavelength of 5.6 mm, power density10.0 mW/cm2 and exposures of 2 and 8 min on dry and imbibed seeds of castor-oil plant results in the highest stimulation of germination processes. Selected mode of irradiation of castor-oil plant seeds with MMR after their long-term storage in plant gene bank contributed to the increase of seed viability that was manifested in the increase of germinating power and germinability of seeds, maximal growth of seedlings, decrease of content of IAA-oxidase enzyme and increase of content of freely soluble proteins in seedling rootlets.