We measured several indexes including the stable organic carbon isotope (δ¹³C_org), the total nitrogen content, the total organic carbon content and the ratio of carbon and nitrogen content of bulk sediments in Lake Fuxian to exploring the sources of organic matters in sediments and the paleoenvironmental significance of δ¹³C_org during the last 5 ka. The results showed the organic matter inputs from both the terrestrial C₃ plants and the aquatic organisms as the main source to the lake sediments have greatly changed during the period of 5000-2300 cal a BP, and changed to the only aquatic input (submerged plants, phytoplankton and algae) since 2000 cal a BP. δ¹³C_org values of bulk sediments in Lake Fuxian were mainly affected by different organic matter inputs. Rapid changes of the δ¹³C_org values during the stage of 2300-2000 cal a BP may indicate that the paleoenvironment of Lake Fuxian basin has experienced a rapid climate event.