1) The variations of flavin adenine dinucleotide(FAD), flavin monomucleotide(FMN) and free riboflavin in control and 600r X-ray irradiated soybean sprout were estimated by the paper chromatographic method. 2) It was found that the formation of riboflavin in soybean sprout was mainly in FAD. 3) There were no great variation of FMN and free riboflavin in soybean sprout during the germination. 4) The moderate amount (600r) of X-ray irradiation accerelated the formation of FAD in soybean sprout during the germination.