Background/Aim: To investigate the effect of polaprezinc (antioxidant) administration and hyperbaric oxygen therapy on radiation-induced intestinal injury. Materials and Methods: Forty-five C57BL/6J mice underwent total body radiation of 2 Gy. Polaprezinc was given in 12 mice, hyperbaric oxygen in 12 mice, and both in 12 mice. The other 9 mice did not undergo any treatment. Mice were sacrificed 2, 4, and 6 h after radiation, and 9 specimens (3 each from the duodenum, jejunum, and ileum) were harvested. Apoptotic intestinal crypt cells were histologically evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. Results: Apoptotic cell number per 1,000 crypt cells was 31.0±6.7 at 2 h, 28.4±5.2 at 4 h, and 32.9±5.1 at 6 h in the mice group treated by radiation alone. Both polaprezinc administration and hyperbaric oxygen therapy significantly suppressed apoptosis. Although the effect of polaprezinc administration on suppressing apoptosis became less over time (4. 9±5.7 and 19.4±13.2 at 2 and 6 h, respectively), that of hyperbaric oxygen therapy was stable regardless of time (23.6±4.8 and 25.8±4.1 at 2 and 6 h). Administration of both polaprezinc and hyperbaric oxygen showed a significant synergetic or additive effect on suppressing apoptosis at 6 h (11.4±10.5, p<0.0035 vs. polaprezinc, p<0.0001 vs. hyperbaric oxygen). Conclusion: Both polaprezinc administration and hyperbaric oxygen therapy are effective in relieving radiation-induced small intestinal damage, and a synergistic or additive effect is expected when using both.