Arsenic (As) has been known a human carcinogen, which is widely distributed in the environment. This study was performed to evaluate the exposure level to arsenic and to determine contributing factors to human exposure of arsenic in Korean adults. Diet intake and urine sample were obtained from 2,044 study subjects older than 19 years of age. Human exposure to the arsenic was assessed by using the concentrations of various arsenic species such as inorganic As (As(V), As(III)), MMA, DMA, arsenobetaine in urine. The concentration of arsenic species in urine was analyzed by HPLC-ICP-MS method. In the arsenic speciation analysis, the geometric mean concentrations were 41.36μg L−1 of arsenobetaine, 24.72μg L−1 of DMA, 1.42μg L−1 of MMA, 2.96 μg L−1 of inorganic As. The levels of various arsenic species in urine were influenced generally by age, smoking, inhabitant area and seafood intake. The consumption of seafood was positively correlated with some of arsenic species such as inorganic As, DMA and arsenobetaine. These findings suggest that the seafood might be a one of major source to the arsenic exposure in Korean adults, and overconsumption of seafood could increase human exposure to inorganic arsenic as well as organic.