A detailed study of the climatic significance of δ¹⁸O in precipitation was completed on a 1500 km southwest-northeast transect of the Tibetan Plateau in central Asia. Precipitation samples were collected at four meteorological stations for up to 9 years. This study shows that the gradual impact of monsoon precipitation affects the spatial variation of δ¹⁸O-T relationship along the transect. Strong monsoon activity in the southern Tibetan Plateau results in high precipitation rates and more depleted heavy isotopes. This depletion mechanism is described as a precipitation “amount effect” and results in a poor δ¹⁸O-T relationship at both seasonal and annual scales. In the middle of the Tibetan Plateau, the effects of the monsoon are diminished but continue to cause a reduced correlation of δ¹⁸O and temperature at the annual scale. At the monthly scale, however, a significant δ¹⁸O-T relationship does exist. To the north of the Tibetan Plateau beyond the extent of the effects of monsoon precipitation, δ¹⁸O in precipitation shows a strong temperature dependence. δ¹⁸O records from two shallow ice cores and historic air temperature data were compared to verify the modern δ¹⁸O-T relationship. δ¹⁸O in Dunde ice core was positively correlated with air temperature from a nearby meteorological station in the north of the plateau. The δ¹⁸O variation in an ice core from the southern Plateau, however, was inversely correlated with precipitation amount at a nearby meteorological station and also the accumulation record in the ice core. The long-term variation of δ¹⁸O in the ice core record in the monsoon regions of the southern Tibetan Plateau suggest past monsoon seasons were probably more expansive. It is still unclear, however, how changes in large-scale atmosphere circulation might influence summer monsoon precipitation on the Tibetan Plateau.