A juniper (Juniperus przewalskii Kom) tree-ring width chronology has been developed from the western-most forest of the Qilian Mountains. Our analyses demonstrate both temperature and precipitation have significant effects on tree growth and that both should be considered in climate reconstruction. Thus a regional drought history (A.D. 1855–2001) is reconstructed by calibrating with a linear interpolation through four Palmer Drought Severity Index (PDSI) grid values nearest the sampling site. Our reconstruction extends the drought history of this area and also reveals that the most severe drought occurred in the 1920s. In the context of the drought history of western China, this extreme drought between 1925–1931 is consistent over a large surrounding region of Northwestern China. Multi-taper spectral analysis reveals the existence of significant 40- to 46-year, 29-year, and 2.1- to 3-year periods of variability. Overall, our study provides reliable information for the research of past drought variability in the Qilian Mountains, Northwestern China.