OPS 35: Health effects of indoor air pollution in LMIC countries, Room 411, Floor 4, August 27, 2019, 1:30 PM - 3:00 PM Backgrounds Although human spent a substantial portion of time, up to 87%, indoors, limited study has focused on the adverse effects of indoor air pollutants on overweight/obesity. Materials and Methods: This study is the sub-study of “Effects of living environments and dietary habits on cardio-metabolic disorders in young adults”. Those who agreed to receive indoor air quality and environmental monitoring were invited to participate this study. During 2017 through 2018, we recruited 127 participants in 60 families. Every participant received cardiovascular health examination and a series of questionnaires. This study conducted 24-hour (24-h) indoor air quality monitoring in 60 households, including particulate matter with aerodiameter < 2.5 and 10 μm (PM2.5 and PM10), total volatile organic compounds (TVOCs), formaldehyde, and carbon monoxide and dioxide (CO and CO2). In this analysis, the association between overweight/obesity indices and indoor air pollution was investigated. Results: Most households’ air quality are within the criteria of indoor air quality Taiwan Environmental Protection Administration. Indoor gaseous air pollution are positively and significantly associated with overweight/obesity indices, body mass index, waist circumference, and body fat percentage measured by bioelectrical impedance analysis (Tanita body composition scanner, Japan). After controlling age, male gender, smoking habit, incense burning, fasting glucose, exercise habit, and education, the indoor 24-h concentration of CO2 and TVOCs were identified as two most important indoor air pollution that positively associated with overweight/obesity. For every increase an interquartile range concentration of indoor TVOCs, the adjusted odd ratio (aOR) (95% CI) for overweight/obesity are 2.26(1.38-3.72) for 12-h (6 pm-6 am) TVOCs and 1.61(1.13-2.30) for 24-h TVOCs, respectively. And, the corresponding aOR (95% CI)for indoor CO2 exposure and overweight/obesity are 1.90(1.22-2.97) for 12-h CO2 and 2.09(1.06-4.11) for 24-h CO2 respectively. Conclusion: Indoor 24-h gaseous air pollution, particularly TVOCs and CO2, are positively associated with participants’ overweight/obesity status.