Background: Preventing recurrence of gastroduodenal ulcers not only helps protect adolescents’ health but also raises their awareness of the importance of diet, rest, and a healthy lifestyle, thereby laying a foundation for long-term health. Objective: This study aimed to describe adolescents’ knowledge of preventing recurrence of gastroduodenal ulcer and to identify factors associated with this knowledge. Methods: A cross-sectional descriptive study was conducted among 92 adolescents aged 10-18 years who received examination and treatment at Thai Nguyen National Hospital. Results: The mean knowledge score for prevention of disease recurrence among adolescents was 21.14±6.17 out of 36 points. Overall, 63% of adolescents had good knowledge of recurrence prevention, whereas 37% had poor knowledge. There was a statistically significant association between a family history of gastroduodenal ulcers and adolescents’ knowledge of recurrence prevention (p<0.05). Conclusion: Adolescents’ knowledge of preventing recurrence of gastroduodenal ulcers was at a moderate level and was significantly associated with a family history of gastroduodenal ulcers (p<0.05). The findings suggest that health education interventions for adolescents, particularly those with a family history of gastroduodenal ulcers, should be strengthened to improve knowledge and help prevent disease recurrence.