Nonstructural carbohydrates (NSC) including soluble sugars and starch is a main energy substance for plant growth and survival. Woody species store NSC to buffer carbon supply and demand asynchronies on different temporal and spatial scales. Although diel pattern of starch concentration is well documented in leaves of herbaceous plants, little is known about that in woody species. Herein, diurnal dynamics of NSC was explored in leaves of two oak trees with different leaf habitats: deciduous Quercus serrata and evergreen Lithocarpus edulis. Diel variations of starch, soluble sugar and NSC concentrations were significant in leaves from Q. serrata, but not from L. edulis. Soluble sugar composition differed between Q. serrata and L. edulis leaves, i.e., Q. serrata had substantial mannose, whereas L. edulis had some myo-inositol. These results indicates that leaf carbon dynamics may differ between deciduous and evergreen broadleaf trees, which deserves further investigations.