This dataset presents bulk organic geochemical data (TOC, TN, d13C, d15N) obtained by EA-IRMS analysis on sediment grain-size fractions from 6 rivers in Chilean Patagonia (n=75). The samples were separated in 10 to 12 grain-size fractions below 1000 µm to assess the influence of grain-size on river sediment geochemistry. Separation was made following the phi scale, using dry sieving for the particles coarser than 32 µm and an Atterberg sedimentation column for the <32 µm fractions. A sub-sample was also dry-sieved at 90 µm.