Tonle Sap Biosphere Reserve (TSBR) is a seasonally inundated freshwater lake in South-East Asia. Nowadays, TSBR is very concerned with many influence factors especially the contaminants (nutrients and heavy metals) in sediment that can cause water damage and water degradation in the lake. In this study, the concentrations of heavy metals and nutrients in fourteen bottom sediment samples in dry season from the lake were investigated to evaluate the level of the contaminant prior to the calculation of the Geo-accumulation Index Value by using the standard of World Surface Rock Average. The concentrations of heavy metals were analyzed by Atomic Absorption Spectrometry (AA-7000F) while the nutrient concentrations were analyzed by Ion Chromatography (LC-20ADsp). The result showed that the increasing concentrations (average) of trace metal elements were observed as followed Fe>Mn>Cu>Cr>Pb >Cd. The concentrations of cadmium in samples were under detection limit whereas the medians of other trace elements were 0.0269 mg/kg, 0.0272 mg/kg, 157.3523 mg/kg, 6.7070 mg/kg, and 0.0385 mg/kg for Cr, Cu, Fe, Mn, and Pb, respectively. The levels of trace metals in sediment samples were under the standard value of World Surface Rock Average, Mean Shale Concentration, and United State Enviromental Protection Agency except for the ion concentration of JS11 that exceed the standard of USEPA. For nutrients, the concentrations of nitrate and ammonia were detected through the IC within the median of 0.38 mg/L and 27.43 mg/L, respectively. The concentrations of ammonia and nitrate in sediment samples were acceptable except for the ammonia concentrations in sample JS2 and JS17 that were over the standard range. However, sediment pollution assessment was undertaken using the Geo-accumulation Index Value. The Geo-accumulation Index Values of heavy metal were negative and they are categorized to be the zero classification of Igeo. Therefore the sediment samples in Tonle Sap Lake are practically unpolluted and the sediment that located in this sampling zone are not strongly affect to the water quality of this study area.