Abstract: Based on the oxygen isotopic values and Li/Ca ratios from ostracod shells of the species of Eucypris inflate in Lake Qinghai, temperature and precipitation variations during the past millennium in this catchment were reconstructed. The good correlation (r=0.5, n=59, p<0.01) between Li/Ca ratios and δ¹⁸O values of ostracod shells indicates that temperature changes corresponded well with precipitation variations during the past millennium. Synchronous variations of temperature and precipitation are also observed in the local meterological records and the climatic parameters inferred from Delingha and Dulan tree ring widths. We believe that the synchronous variation as such is a sole feature of East Asian summer monsoon, although the factors controlling this featue deserve further study.