The xylem hydraulic conductivity of the panicle neck is considered to be responsible for the maintenance of the panicle water status which is not under the stomatal control in rice. To clarify the hydraulic properties of the panicle neck, the water transport function of the panicle neck and panicle characters were examined in 12 paddy and 8 upland rice genotypes originating from various countries. The hydraulic conductivity (K) under full hydration increased with the increase in the number of spikelets per panicle (N_s), panicle area (A_p, projected area of a whole panicle which was considered to be an indicator of the evaporative surface) and the number of large vascular bundles of the panicle neck (N_b) in paddy rice. A large variation in K was also detected in upland rice, but not in N_s and N_b, and the relationships of K with N_s, A_p and N_b were not significant. On the other hand, there was a significant relationship between the diameter of the large xylem vessels and K in the paddy and upland rice genotypes. A positive relationship was found between K/A_p or K/N_s (ability of the xylem of the panicle neck to supply water per unit evaporative surface or to one spikelet) and the size of the spikelet (A_s, calculated as A_p/N_s) . Since upland rice has large spikelets, the value of K/A_p was higher in upland rice. The xylem became vulnerable as N_s increased in paddy and upland rice genotypes. These results suggested that upland rice was able to cope with dry environments not because of a less vulnerable xylem to dysfunction but due to the higher hydraulic conductivity of the xylem. The relationships found in this study may enable to estimate the hydraulic properties based on the panicle characters.