Radiation-induced lung injury (RILI) is one of the common complications of radiotherapy for chest tumors and nuclear radiation accidents. The excessive reactive oxygen species induced by radiation is the main mediator. So far, the effective prevention and treatment for RILI are still lacking. Astaxanthin is a carotenoid that belongs to red natural lutein family and is commonly found in Marine organisms such as shrimp, oysters and salmon. It has been confirmed that astaxanthin has strong antioxidant and anti-inflammatory properties, therefore we speculated that astaxanthin may be a potential treatment for RILI. First, with a mice model of RILI, the protected effects of astaxanthin were observed. Furthermore, the experiments in vitro were performed by detecting apoptosis. As a result, astaxanthin protects the RILI, inhibits the process of pulmonary fibrosis, and reduces the elevation of inflammatory factors. The experiments in vitro demonstrated that astaxanthin could reduce radiation-induced apoptosis and especially inhibit activation of apoptosis pathway. In conclusion, astaxanthin could protect RILI of mice, which is mediated by inhibiting activation of apoptosis pathway.