Abstract: Leaf vein is an important structure for plant photosynthesis and water transportation. In this study, leaf vein density and photosynthetic characteristics were examined to explore the relationship between them in Sorghum bicolor and Perilla frutescens seedlings. Compared with perilla, sorghum leaves had higher leaf vein density, stomatal conductance (G_s) and leaf hydraulic conductance (K_leaf). While perilla leaves had higher stomatal density than sorghum leaves. For sorghum leaves, the proportion of stomata on the adaxial side accounted for 38.4% of the total stomata, which was significantly higher than that in perilla leaves. Sorghum leaves developed with higher vein density had higher net photosynthetic rate, whereas perilla leaves developed with lower vein density have lower net photosynthetic rate. Therefore, high photosynthetic rate in sorghum may be related to high vein density. However, there was no rigidly collaborative variation between leaf vein density and stomatal density. These conclusions are important for the study of photosynthetic adaptation to water availability.