The profound impacts exerted by climate warming on the Tibetan Plateau have been documented extensively, but the biogeochemical responses remain poorly understood. This study was aimed at seasonal variations of total organic carbon(TOC) and total organic nitrogen(TON) in stream water at two gauging sections(TTH, ZMD) in the upper basin of Yangtze River(UBYA) and at fourgauging sections(HHY, JM, JG, TNH) in the upper basin of Yellow River(UBYE) in 2013. Results showed that concentrations of TON exhibit higher values in spring and winter and lower values in summer. TOC exhibits higher concentrations in spring or early summer and lower concentrations in autumn or winter. Seasonal variations of TOC and TON fluxes are dominated by water flux. In total, the UBYE and UBYA delivers 55,435 tons C of organic carbon and 9,872 tons N of organic nitrogen to downstream ecosystems in 2013. Although the combined flux ofTOC from UBYA and UBYE is far lower than those from large rivers, their combined yields is higher than, or comparable with, those from some large rivers(e.g. Nile, Orange, Columbia), implying that organic carbon from the Tibetan Plateau may exert a potentially influence on regional and/or global carbon cycles in future warming climate. The profound results exerted by climate warming on the Tibetan Plateau have been documented extensively, but the biogeochemical responses remain poorly understood. This study was originally at seasonal variations of total organic carbon (TOC) and total organic nitrogen (TON) in stream water at two (TTH, ZMD) in the upper basin of Yangtze River (UBYA) and at fourgauging sections (HHY, JM, JG, TNH) in the upper basin of Yellow River (UBYE) in 2013. Results showed that concentrations of TON exhibit higher values ​​in spring and winter and lower values ​​in summer. TOC exhibits higher concentrations in spring or early summer and lower concentrations in autumn or winter. Seasonal variations of TOC and TON fluxes are dominated by water flux. In total, the UBYE and UBYA delivers 55,435 tons C of organic carbon and 9,872 tons N of organic nitrogen to downstream ecosystems in 2013. Although the combined flux of TOC from UBYA and UBYE is far lower than those from large rivers, their combined yi elds is higher than, or comparable with, those from some large rivers (eg. Nile, Orange, Columbia) implying that organic carbon from the Tibetan Plateau may exert a potentially influence on regional and / or global carbon cycles in future warming climate.