Seasonal changes of water relations parameters were obtained from p-v curves in leaves of Quercus grosseserrata and Quercus acutissima. The osmotic pressure at full hydration, no, and osmotic pressure at incipient plasmolysis, trp, were high in newly emerged leaves but decreased with leaf development in each of the species. Water deficit at turgor loss was 10 to 20% in each of the species during the growing season. Maximum bulk elastic modulus in cell walls at full turgor, Emax, rises rapidly with leaf development before senescence in each of the species. Seasonal change of number of osmoles solute in symplasm per dry weight, Ns/DW, was higher in Quercus grosseserrata leaves than Quercus acutissima leaves, while relative water content (Vp/Vo, RWC^*, Vo/Vt) was relatively constant in each of the species.