Leaf hydraulic conductance (K leaf) and mesophyll conductance (g m) both represent major constraints to photosynthetic rate (A), and previous studies have suggested that K leaf and g m is correlated in leaves. However, there is scarce empirical information about their correlation. In this study, K leaf, leaf hydraulic conductance inside xylem (K x), leaf hydraulic conductance outside xylem (K ox), A, stomatal conductance (g s), g m, and anatomical and structural leaf traits in 11 Oryza genotypes were investigated to elucidate the correlation of H2O and CO2 diffusion inside leaves. All of the leaf functional and anatomical traits varied significantly among genotypes. K leaf was not correlated with the maximum theoretical stomatal conductance calculated from stomatal dimensions (g smax), and neither g s nor g smax were correlated with K x. Moreover, K ox was linearly correlated with g m and both were closely related to mesophyll structural traits. These results suggest that K leaf and g m are related to leaf anatomical and structural features, which may explain the mechanism for correlation between g m and K leaf.