The room temperature adsorption of water on clean and sodium predeposited InP(lll) surface has been studied by UPS and HREELS. The sticking coefficient of water on InP(lll) surface increases significantly as the surface is covered with 0.3 moiiolayer of sodium. This sticking coefficient enhancement could be shown to be related to the charge transfer between the sodium atoms and the surface phosphorous atoms. Water species adsorb On the surface mainly in the form of undissociated molecules. The existence of P-H bond related loss energy peak at 282 meV observed in HREELS suggests that a portion of water molecules may interact with sodium atoms predeposited on the surface or possibly decomposed on the surface to release free hydrogen atoms which could make bonding with surface phosphorous atoms.