The ages of drift boulders are usually very difficult to be dated directly, and it is harder to know whether the boulders have been re-transported or rolled over since their formation. The authors think that not only the formation chronology but also the re-transportation history of boulders can be determined by measuring the cosmogenic isotopes at different parts of the boulders. A case study has been carried out on a drift boulder by using the isotope 10Be. Based on the measurement and analyses of the cosmogenic isotope 10Be of a drift boulder, which is located in the vicinity of Haizishan in the southeastern margin of the Qinghai-Tibet Plateau, we may conclude that the boulder was formed during the glacial stage before the last (186~128 ka BP) and was re-transported and rolled over during the last glacial stage. There have been at least two stages of glacial development since 200 ka BP in the vicinity of Haizishan, corresponding to Stage 6 and Stages 4~2 of the deep-sea oxygen isotopes, respectively. This method, using other cosmogenic isotopes as well, can be applied to stone blocks or gravels formed by other agents. Therefore, it provides an important method to study glacial processes, activities of debris flow and rock collapse etc.