Abstract: We study the DOC concentrations, the UV-Vis absorbance, fluorescence and the molecular weight of the dissolved organic matter in the sediment pore water of Erhai Lake.DOC concentration has a high value at the sediment-water interface, with a sharp decrease within the depth of 6 cm, and, then, increases later.The vertical distributions of a₂₅₄, a₂₈₀ and fluo-rescence intensity at Ex=335 nm are in agree with the distribution of DOC.The E3/E4 values range from.to 6 and most of the values are less than 3.5, which means that the DOM in sediment pore water has relatively high humification, aromaticity and molecular weight.f_450/500 values range from 1.48 to 1.59, showing the terrestrial nature of the majority of the sediment pore water DOM.Through the HPSEC results, all the sediment pore water DOM show a multi-modal distribution of the molec-ular weight.Weight-average molecular weight (M_w), which ranges from 1462 to 1953 Da, and number-average molecular weight (M_n), which ranges from 547 to 900 Da, vary a little along the depth and mainly have a trend of increase.The poly-dispersity, ρ (the ration of M_w to M_n) ranges from 2.02 to 3.05, which suggests that the pore water DOM resides in a rela-tively wide size distribution.In general, the geochemical characteristics of sediment pore water DOM are attributed to the changes in redox chemistry occurrs as a function of the sediment depth, partial mineralization of particulate organic matter as a result of the biotic or abiotic reduction and the effect of metal oxide through the dissolution and formation process.