Objective: Previous studies focused primarily on drivers or front-seat passengers in motor vehicle accidents. Recent research has shown improvements in front-seat occupant protection. This study examined the risk factors contributing to severe injury in rear-seat occupants. Methods: This study was conducted retrospectively. The variables related to the crash data were acquired from the Emergency Department-based Injury In-depth Surveillance registry and electronic medical record of the authors’hospital between 2019 and 2020. Multivariate logistic regression analysis was used to identify the risk factors contributing to severe injury in rear-seat occupant. Results: One hundred and forty rear-seat occupants were analyzed. The occupants were categorized by the abbreviated injury scale into severe (n=39; 27.9%) and non-severe injury (n=101; 72.1%). The collision with a large-size vehicle (odds ratio [OR], 4.278; 95% confidence interval [CI], 1.617-18.000; P=0.015) and fixed objects (OR, 3.459; 95% CI, 1.347-8.883; P=0.049) was independently associated severe injury. Seatbelt use was also an independent risk factor of severe injury (OR, 2.649; 95% CI, 1.178-5.940; P=0.018). Common severe injuries encountered in rear seats were chest (12.1%), spine (9.3%), and abdomen (5.7%). Conclusion In contrast to the fact that seat belt use reduces the severity of injuries, seatbelt use was associated with severe injury in this study. Further research will be needed to assess the effects of seatbelt use. In addition, awareness should be raised about the relationship between the accident mechanism, seatbelt use, and the commonly injured body region.