Purpose <p>Physical activity is a core component of diabetes management. However, evidence linking physical activity levels to health-related quality of life (HR-QOL) in adults with diabetes remains limited, particularly when measured using the Health-related Quality of Life Instrument with 8 Items (HINT-8). This study examined the association between physical activity level and HR-QOL and explore subgroup patterns among Korean adults with diabetes.</p> Methods <p>We analyzed nationally representative data from the 8th Korea National Health and Nutrition Examination Survey (2019–2021). Adults with diabetes were identified using fasting plasma glucose, glycated hemoglobin, or prior diagnosis/medication use. HR-QOL was assessed using HINT-8, a preference-based instrument developed to reflect the health preferences of the general Korean population. Physical activity levels were classified as low, moderate, or high using the Global Physical Activity Questionnaire. Associations were examined using survey-weighted linear regression.</p> Results <p>Among 1,590 adults with diabetes, 59.3% reported low physical activity. Compared with the low-activity group, high physical activity was significantly associated with higher HINT-8 scores (β = 0.024; 95% CI 0.008–0.039). Although the moderate activity group showed a positive trend (β = 0.010; 95% CI − 0.004 to 0.023), it did not reach statistical significance.</p> Conclusion <p>High physical activity levels may be associated with better perceived health status among Korean adults with diabetes, highlighting the importance of supporting adults with diabetes to achieve higher overall physical activity levels.</p>