The focus of this study is to use the record of sedimentary organic processes to reconstruct the environment of Lake Azuei over the last millennium. Bulk and isotopic organic matter (OM), stratigraphic markers, and a chronological model based on 11 14C ages and 6 210Pb analyses from a shallow sediment core were used to support this reconstruction. TOC and TN contents reveal that the sediments of Lake Azuei are quite poor in organic matter. The δ13C and C/N results suggest that a mix of algae and C3 plant material dominates OM in lake sediment. It appears that denitrification is connected to physical and chemical conditions, such as temperature and/or the availability of nitrate and organic matter. Three different sedimentary environments are recognized based on δ13C vs C/N cross diagram. During the MCA1 (1000-1050 CE) and LIA (1400-1800 CE) periods, a decrease in TOC and TN as well as in plankton-derived OM occurred. This was accompanied by an increase in δ15N, which suggests denitrification due to suboxic conditions, likely caused by an increase in lake water temperature and dry conditions. A second sedimentary environment, applying to the MCA2 (1050-1100 CE) and CWP (1800-2000 CE) periods, was characterized by the increase of TOC and TN values, and decrease of δ13C and δ15N values. This is chiefly attributable to more organic material input which is derived from C3 terrestrial vegetation growing around the lake. A decrease in δ15N indicates a decrease in denitrification, further suggesting an increase in the input of organic matter. Sedimentation during these periods occurred when there was more transport related to wet conditions. The third sedimentary environment applies to the MCA-LIA (1150-1400 CE) transition period and is characterized by a high variability of COT, δ13C and δ15N. The organic matter deposited during this period appears to be a mixture of material originating from both autochthonous phytoplankton and allochthonous C3 plant. There was climate instability during this period, with alternations between wet and dry conditions, and thus likely variations in the lake level.