Amylomaize starch irradiated with gamma rays up to 10 Mrad, was examined for the digestibility and compared with that of normal corn starch. 1) In the case of in vitro digestion with pancreatic a-amylase, the digestibility of both amylomaize and normal corn starches were elevated with increasing in radiation dose levels. Amylomaize starches irradiated at 0 and 10 Mrad were incubated with a-amylase for 24 hr and degraded 16.7% and 18.4%, respectively. Those of normal corn starches were 48.5% and 54.4%, as well. In the case of digestion with the extract of rat small intestine as degrading enzymes, the digestibility of 10 Mrad irradiated amylomaize and normal corn starches became slightly higher than those of the respective non-irradiated counterparts . 2) In vivo apparent digestibility of amylomaize and normal corn starches in growing rats showed a tendency to be lowered by the radiation, and a concomitant increase in weights of both feces and cecum contents was observed after feeding period of 28 days . From the results of in vivo observations, it seemed that both starches on the radiation received some structural modification, in which they could not be digested by the enzymes. However, amylomaize starch was less sensitive to this treatment than normal corn starch .