Variations in organic carbon and total nitrogen concentrations, and relationship between C/N ratio and isotope composition (δ~(13) C and ?δ~(15) N) were studied in riverine suspended solids from the Abukuma River system in Japan. The samplings were carried out at the upper, middle and lower reaches before and after rain event by typhoons in 2011-2013. There is a negative correlation between C/N ratio and ?δ~(13) C, and C/N ratio and ?δ~(15) N after the Typhoon Roke in 2012. On the other hand, in normal flow condition, there is no correlation between C/N ratio and ?δ~(13) C of suspended solids. These results indicate that the transport of particulate organic matter (POM) in these river basins is controlled by their watershed conditions and supply of POM in rain event.