This paper reviewed the transport behavior of 137Cs in river systems of Fukushima Prefecture, Japan after the Fukushima Dai-ichi Nuclear Power Plant accident during 2011–2014. Total radioactivity of 137Cs in water samples from the Abukuma River and small watershed river systems in eastern Fukushima, Hama-dori region, decreases exponentially with increasing time after the accident at normal flow condition. Higher radioactivity was found at higher flow condition caused by rain events. Particulate phase of 137Cs in river waters ranged from 60 to 99% to total radioactivity. Apparent distribution coefficient (Kd value) of 137Cs was 102 to 103 l g-1. The annual export of 137Cs from land to coastal ocean was estimated as 1010 to 1013 Bq in the river basins on the basis of field research data. These results indicate that major part of 137Cs is exported as particulate forms associated with suspended solids in the river waters.