Leaf wettability, adhesion or repulsion of water drops, varies greatly among species and plays an important role in plant–soil hydrological relations. This study aimed to examine the variability in leaf wettability among species in different habitats and growth periods, and their relationships with plant surface water retention in the semiarid Loess Plateau of China. The leaf adaxial and abaxial contact angles, the surface water retention of leaves and individual plants, and general plant traits of 68 species belonging to 28 families were examined from May to August in 2017. Results showed that leaf water contact angles ranged from 27.3° to 133.4° and leaves with higher contact angles normally had lower variation coefficients. Leaf wettability was affected by internal properties (including leaf side, family, and leaf age) and external conditions (growth period), whereas the life form and slope aspect did not show significant effects. There were 47 species having higher contact angles on adaxial than abaxial surfaces, and the differences were significant in 23 species. Gramineous and leguminous species were more unwettable than compositae and rosaceous species. New leaves were more unwettable than old leaves. Surface wettability increased from May–June to July–August period. Leaf wettability was positively correlated with leaf surface water retention and was the best predictor of individual plant surface water retention compared with other plant traits. Leaf wettability showed interspecific differences associated with family and growth stage and can be a considerable variable in predicting canopy interception and evaluating vegetation hydrological function in drought environments.