Despite the development of radiotherapy machines and technologies, a proportion of patients suffer from radiation-induced enteritis or oral mucositis. It has been reported that hangeshashinto has been used for not only enteritis but also oral mucositis. This study reports the effect of hangeshashinto on enteritis or oral mucositis caused by radiotherapy. Three patients with enteritis and 5 patients with oral mucositis were treated with hangeshashinto at a dose of 7.5 g/day. The severity of enteritis or oral mucositis was evaluated using the Common Terminology Criteria for Adverse Events version 4 and Numerical Rating Scale both before and after hangeshashinto treatment. After the treatment with hangeshashinto, 3 of 5 patients with oral mucositis and 2 of 3 patients with enteritis showed apparent improvement. In conclusion, it is important to control the side effects of radiotherapy, which lead to improved tumor control rates. Prospective randomized studies are necessary to confirm the findings of this case series study.