An investigation on the structures and the excited-state porton-tranfer reaction has been carried out for size-selected 7-hydroxyquinoline(7HQ)-methanol hydrogen-bonded clusters in supersonic jets. The structures of the clusters were determined based on the analysis of the fluorescence-detected IR spectra in the OH stretching region and by density functional theory calculations. Two isomers were found to exist for 7HQ-(CH₃OH)₁. One has the form in which the OH group of 7HQ is hydrogen-bonded to the oxygen of CH₃OH, and the other has the form in which the OH group of CH₃OH is hydrogen-bonded to the nitrogen of 7HQ. For 7HQ-(CH₃OH)₂ and -(CH₃OH)₃, their structures were determined to be “enol bridge” form, in which one end of a chain-formed methanol cluster is hydrogen-bonded to the OH group and the other to the nitrogen of 7HQ. Photoinduced excited-state proton-transfer reaction was investigated by measuring the dispersed fluorescence spectra for the clusters. Among them, a visible emission with a maximum at ∼530 nm, which coincides with the tautomer emission of 7HQ generated in methanol solution, was observed for the enol bridge 7HQ-(CH₃OH)₃ and larger clusters. This result presents a direct evidence for the enol bridge form 7HQ-(CH₃OH)₃ to be a precursor for the proton-tranfer reaction in solution.