This study identified factors influencing diet-related quality of life (QoL) among hemodialysis patients by age. In a cross-sectional correlational study in South Korea, 175 participants from two age groups—20–59 years and 60 years and above—completed self-report questionnaires assessing demographic and health-related characteristics, eating status, subjective health status, disease-related factors, dietary knowledge, and xerostomia severity. Findings indicated that the predictors of diet-related QoL included subjective health status and regular eating status (20–59 years) and self-efficacy, attitude toward hydration behaviors, and exercise (60 years and above). In order to improve the diet-related quality of life of dialysis patients, young adults need to focus on their physical health and regular meals, and the elderly need a differentiation strategy that considers psychological factors such as self-efficacy and attitude toward pollination.