Background: Dietary intake is important for physical and mental health. Objectives: The purpose of the study was to investigate the effect of dietary behaviors on psychological well-being and mental distress in a large cross-national sample of university students from five ASEAN countries (Indonesia, Malaysia, Myanmar, Thailand, and Vietnam) Methods: In this cross-sectional survey, 3357 university students (Mean age = 20.5 years, SD = 1.6), who were randomly selected, responded to a questionnaire including measures of dietary behaviors, psychological well-being, and mental distress. Results: In analysis of covariance, adjusted for age, sex, subjective socioeconomic status, country, body mass index (BMI), and physical activity, positive dietary behaviors (fruit and vegetable consumption, daily breakfast, fat avoidance, and eating foods high in fiber) were associated with happiness, life satisfaction, and self-reported health. Fruit consumption and regular breakfast were negatively associated with depression and traumatic stress symptoms. Unhealthy dietary behaviors (soft drinks, fast foods, and eating snacks) were associated with unhappiness, low life satisfaction, and depression symptoms. Conclusions: Overall, the study found some evidence indicating that healthier dietary behaviors were associated with higher psychological well-being and lower mental distress, suggesting that a diet intervention may be helpful in preventing or alleviating mental distress in this ASEAN university student population.