Purpose: This study examined the impact of adolescents' dietary behavior on their quality of life using the nutrition quotient for adolescents (NQ-A) for some high school students in Seoul. Methods: The subjects were 176 high school students living in Seoul. The NQ-A was used to assess the dietary quality, and the quality of life was assessed by categorizing it into life satisfaction, environment, health, participation and safety, leisure activities, and emotional factors using survey questions validated through previous studies. Results: The NQ score of the survey subjects was 49.30 points. Based on the NQ scores, 7.4%, 46.6%, and 46.0% of participants were categorized as the 'high', 'medium', and 'low' groups, respectively. The total NQ score and balance, diversity, and practice factor scores were positively correlated with life satisfaction, environment, health, participation and safety, and leisure activities among the quality of life subscales. Regression analysis showed that the total NQ score was positively associated with life satisfaction, health, leisure activities, and emotions; the moderation factor was negatively associated with life satisfaction and health. The balance factor was positively associated with the environmental factor. The practice factor was positively associated with health, leisure activities, and emotions, and the environment factor was negatively associated with emotions. Conclusion: These results show that adolescents' quality of life is closely related to their diet, so it is necessary to maintain a balanced and varied food intake and desirable eating behaviors to improve adolescents' quality of life. Furthermore, adolescents' quality of life is influenced by other factors. Therefore, further research is needed to assess the quality of life, including dietary factors, as well as physical, emotional, psychological, and social development.