Abstract: The stable isotopic compositions of precipitation exhibit great diversities in different areas and seasons due to in fluences of multiple factors,such as temperature,evaporation,rainfall amount,moisture source and others.The Local Meteoric Water Line(LMWL) is established for Chongqing,China using precipitation samples collected between April 2006 and September 2008,as the result of a 29-month field campaign on the campus of Southwest University.Both D and ¹⁸O values in rainwater exhibit sign ificant seasonal variations,having higher values in winters and lower one in summers.The result also indicates that the moisture source is the primary factor for determining the isotopic compositions in local precipitation in this monsoonal region.In addtion,the evaporation is another important factor in controlling the isotopic compositions of rainwater during short-term rain events.