The aim of this study is to determine the exposure concentration of tetrabromobisphenol A(TBBPA) in southwestern coast and their photodecomposition rate. Also, it is to identify the radical species of the photodecomposition of TBBPA and their reactive byproducts using the electron spin resonance(ESR) method. TBBPA was not detected in any of the sea water samples from Mokpo, Gunsan, or Goheung. The sediment samples from Mokpo contained not detection(N.D)∼50.0 ng/g dry wt., while those from Gunsan contained N.D∼28.5 ng/g dry wt. and those from Goheung contained N.D∼7.3 ng/g dry wt. The photodecomposition rates were 2.56 × 10-6/hr by visible light(400 nm), 7.98 × 10-6/hr by ultraviolet light(300 nm <), and 6.78 × 10-6/hr by sunlight. Also, we confirmed that singlet oxygen and hydroxyl radicals are the key reactive oxygen species at wavelengths greater than 400 and 300 nm, respectively. This study shows that the main byproducts formed during irradiation at wavelengths above 300 nm are 2,6-dibromobenzosemiquinone radical(2,6-DBSQ·-) and g-value 2.0048 doublet spectrum.