The protective effect of beta-carotene against radiation injury to the small intestine of abdominally radiated mice (15 Gy) was examined with administration given pre-radiation, during (pre- and post-) radiation, and post-radiation. In the beta-carotene group, the ratio of villus length to crypt was significantly greater in comparison with the radiation only group at 2 days after radiation. At 7 days after radiation, the ratio of necrotic cells in the crypt vs. the total was significantly lower, and the ratio of necrotic cells in the villus vs. the total was significantly greater with beta-carotene administration, which indicated that beta-carotene accelerated recovery from radiation injury. Each group administered beta-carotene showed a significant radioprotective effect, with pre-radiation administration yielding a smaller effect than administration during radiation and post-radiation. It is concluded that pre-, during, and post-radiation administration of beta-carotene protected against radiation injury of the small intestine and accelerated recovery from it.