OBJECTIVES:  To investigate trends of the quality of life in South Korean adults aged 19 and older using Korean National Health and Nutrition Examination Survey (KNHANES). METHODS:  This study used the 2007-2010 Korean National Health and Nutrition Examination Survey (KNHANES), a nation-wide survey on various health-related questions for a nationally representative sample of the non-institutionalized population of South Korea.  Quality of life (QOL) was measured using the EQ-5D instrument and the QOL index scores were calculated based on Korean version of the score calculation algorithm.  Trends of QOL index and factors influencing QOL index scores were analyzed using analysis of variance and ordinal least square regression after adjusting for the study variables.   RESULTS:  A total of 23,777 adults were identified during 2007 to 2010.  Mean age was 44.7 years and 50.5% were female and 68% were graduated from high schools or colleges and 31% had the body mass index ≥25. Hypertension was most prevalent chronic disease (16.5%), followed by arthritis (13.3%), hyperlipidemia (7.0%), and diabetes (6.3%). The overall EQ-5D index scores have been slightly increased from 0.94 to 0.96 during 2007-2010. Male adults had higher EQ-5D index scores than female (0.96 vs. 0.92).  Elderly (age≥60) had significantly lower EQ-5D index scores (score ranges: 0.02 to 0.11) than young adult (age=19-29) after adjusting for other variables.  EQ-5D index scores were significantly reduced by stroke (reduced by -0.10), arthritis (reduced by -0.05), cardiovascular disease (reduced by -0.04), and diabetes (reduced by -0.02). CONCLUSIONS: QOL in South Korean adults was significantly reduced by chronic diseases and age. Despite national efforts to detect and treat chronic diseases at early stage of disease, significant reduction in QOL due to chronic diseases still exist.  It is emphasized the need for implementation of effective public health programs for decreased prevalence of chronic diseases.