Fieldwork along the western Haiyuan fault, where it cuts young glacial landforms in the Leng Long Ling range (Qinghai, northeastern Tibet), yields new constraints on its long-term left-slip rate. Our mapping near 101.85¿E, based on aerial photographs, 1/50,000 topographic maps, and SPOT images, shows glacial valley edges and lateral moraines offset ~200 m by the fault. Quartz-rich cobbles were sampled on top of one moraine for in situ 10Be and 26Al cosmogenic nuclide dating. Among 12 dated samples, the 6 oldest show ages clustering at 10,300 ¿ 339 years. This age probably reflects the time of last reshaping of the moraine before the valley glacier withdrew south of the fault around the end of the Younger Dryas (≃11,000 years B.P.). Assuming that the 200 ¿ 40 m moraine offset started to be recorded after glacial retreat across the fault constrains the late Pleistocene slip rate on the Leng Long Ling segment of the Haiyuan fault to be 19 ¿ 5 mm/yr.