To obtain the seasonal characteristics and the size distributions of chemical compositions of the atmospheric aerosols in urban seaside area of eastern central Japan, size-separated aerosol samples were collected at Tokaimura (36.27¿N, 140.36¿E) using an Andersen type sampler during July 2002 to July 2003. A maximum mass concentration of aerosols (about 50 ¿g/m3) during April and May and a minimum one (about 13 ¿g/m3) in January and a size distribution with two peaks at 0.43--1.5 ¿m and 3--8 ¿m were observed. The size-separated aerosols were divided into water-soluble and water-insoluble fractions, and Na+, Cl-, NH4+, NO3-, SO42-, Mg2+, Ca2+, and Pb2+ in water-soluble fraction and Na, Al, Ca, Mg, Fe, Pb, Th, and U in insoluble fractions were analyzed. Then, the seasonal variations and the size distribution in mass concentration of each chemical composition and the chemistry of sea-salt particles were also studied in detail. Our results showed that (1) considerable amount of soil-derived particles was supplied from dust storm incident in China, (2) there was a loss of chlorine in sea-salt particles and this loss was compensated with the replacement by SO42- and NO3-, (3) the size distribution of Th and U showed a bimodal curve with two peaks at 0.43 ¿m and bigger than 3 ¿m and these two elements in the atmosphere seem to have two sources, and (4) aerosols contained both soluble and insoluble Pb and the soluble one became much lower in the colder seasons. The concentrations of soluble Pb showed a close relationship with anions such as Cl- and SO42-.