We investigated the diurnal variation of stomatal conductance to water vapor (Gs) and leaf water relations in nine tropical rainforest canopy tree species in Malaysia to investigate the sensitivity of stomatal conductance to VPD and its dependence on leaf water relations. We focused on the effect of wood anatomical properties on the stomatal sensitivity to VPD. Negative correlations were obtained between leaf-to-air VPD (VPDleaf) and Gs for all species, in which interspecific variation was obtained for the sensitivity of Gs to VPDleaf with the range of VPDleaf being 1.2 - 5.9 kPa. Species with a large mean xylem vessel diameter had a high sensitivity of Gs to VPDleaf. Although significant variations were obtained among the species for leaf water relations, such as relative water content at the turgor loss point (RWCtlp) and potential at the turgor loss point (Ψtlp), these water relations were not related to the stomatal sensitivity to VPDleaf. In the wet tropical forest in the present study, VPDleaf was the main regulator of Gs in the nine tree species. The high sensitivity of Gs to VPDleaf in the trees with a large vessel area may contribute to the maintenance of an adequate leaf water status, e.g., high levels of Ψleaf, throughout the day, across a period of varying air temperature.