Abstract: The stable isotope of organic carbon (δ¹³C) in lacustrine sediment is an important environmental proxy and is widely used in lake sediment and environmental change studies, but its response to environmental change is comparatively complicated. In this study, we use a 216 cm lake sediment core from Chen Co, located in Southern Tibet to distinguish the environmental significance of organic matter δ¹³C. The results indicate that the fluctuation of organic matter δ¹³C well responds to the cold/warm variation of the lake areas; the corresponding way is that δ¹³C had relatively low values during the warm periods and high values during the cold periods. Based on the variation of δ¹³C as well as other geochemical proxies such as total organic carbon (TOC), hydrogen index (HI), and carbon hydrogen ratio (C/N), the cold/warm fluctuation of the past ca.1 400 years in the study area was discussed, four warm periods and four cold periods as well as some interims between them were distinguished. The four warm periods corresponded to "warm period in Sui and Tang Dynasty", "Medieval Warm Period"(including the two middle warm periods) and "Global Warming in 20th Century" respectively; while the latter three cold periods correlated to the three cold periods of the Little Ice Age and the time range are 1460-1510AD, 1660-1770AD and 1850-1900AD, respectively. The warm/cold periods indicated by δ¹³C of CC1 core have some similarity to those from other studies by ice core, tree rings, phenological data, historical records and measurement data in other areas on Tibetan Plateau and the eastern part of China, reflecting the lacustrine sediment organic matter δ¹³C is effective as a environmental proxy while the environmental change in Southern Tibet area is similar to the counterparts in other areas.