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Salix gordejevii (SG) is a pioneer bush that settles mainly in the margin of moving sand dunes in Horqin Sandy Land, Inner Mongolia, China. This study examines its heat and drought tolerance compared with Salix babylonica (SB), another willow plant common in northern China. Detached leaves were submitted to six temperature treatments (25, 30, 35, 40, 45, 50 degrees C) for 60 minutes and six osmotic treatments (0, -0.25, -0.5, -0.75, -1.0, -1.25 MPa) for 24 hours, respectively. Then the cell membrane permeability (indicated by electrolyte leakage) and maximal quantum yield of photosystem II (PS II) (measured as F-v/F-m) were assayed. Membrane permeability in SG was increased more sharply by thermal treatment above 45 degrees C than in SB, and F-v/F-m in SG was significantly smaller due to thermal treatment above 40 degrees C. For osmotic treatment, membrane permeability was always smaller and F-v/F-m was significantly larger in SG when osmotic potential was lower than -0.75 MPa. Taken together, these results suggest that SG has a higher capacity for drought tolerance and a lower capacity for heat tolerance than SB, indicating that SG inhabits desert environments mainly due to its high drought tolerance.