Photosynthesis and hydraulic traits enable plants to acquire carbon and water, which are closely coupled in tree leaves. It remains unclear how these traits are coordinated across species and environmental gradients. We examined the relationship between photosynthetic traits and leaf hydraulic conductance (Kleaf) in two Fagaceae species (Quercus serrata and Q. crispula) along an elevational gradient (278 m to 800 m, and 791 m to 1192m, respectively) and interspecific difference in Nikko, Japan. There were no significant elevational trends of maximum photosynthetic rate (Amax), stomatal conductance (gsc), mesophyll conductance, and Kleaf. However, we found a positive Amax-Kleaf relationship in the pooled data from different elevations in both species. The correlations of Amax with Kleaf might contribute to the efficient carbon gain because the high Kleaf allows high gsc to obtain enough CO2 for the high photosynthetic capacity. Further, interspecific difference analysis showed that Q. serrata had lower Kleaf than Q. crispula due to the limited hydraulic capacity of the outside of xylem pathway (Kox) in Q. serrata. Higher leaf thickness and lower leaf vein density of Q. serrata likely caused longer water movement in frictional mesophyll tissue, reducing Kox. The higher Kleaf and Kox of Q. crispula compensate for the lower temperature and shorter growing season at high altitudes, enhancing photosynthesis and growth when conditions allow.