The Asthma Control Test (ACT) is a patient-completed questionnaire developed to assess asthma control. Health-related quality of life (HRQL) in asthmatics has shown relatively low correlations with parameters of asthma control and the relationship between the ACT and HRQL in asthmatics is yet unclear. Because revalidations of translated versions of questionnaires are critical for its utilization, we first sought to validate the Korean version of ACT and then to evaluate the relationship between the ACT and HRQL. Patients (n=117) completed the ACT and asthma-related quality of life questionnaire (AQLQ) at 3 physician visits. Pulmonary function was measured and an asthma specialist rated asthma control. The Korean version of ACT was found to be reliable, valid, and responsive to changes in asthma control over time up to three consecutive visits. ACT scores correlated significantly (p=0.001) with symptoms domain (r=0.72), activity domain (r=0.65), emotional domain (r=0.69), and environmental domain (r=0.67) of AQLQ. In conclusion, the Korean version of the ACT was found to be a reliable and valid tool for measuring asthma control, and to correlate well with AQLQ scores. Moreover, the ACT was responsive to changes in AQLQ scores over time.