[en] Ionization energies of Li_n(OH)_n-1 (n=2-5) clusters are reported. Photoionization time-of-flight mass spectrometry of a jet-cooled cluster beam are applied to the determination of the ionization energies of these clusters, varying the photon energy. Clusters are generated by laser ablation of lithium metal in the presence of water vapor. The ionization energies are determined as 4.32, 4.10, 3.29, and 3.58 eV for the clusters with n=2-5 respectively. Ab initio molecular orbital theory and density functional theory calculations are carried out to obtain theoretical ionization energies and structures of stable isomers. Good agreement has been found between experimental and theoretical values for the most stable structural isomer in each cluster size. In particular, measured ionization energy suggests that symmetry breaking occur in the most stable Li₃(OH)₂ isomer, indicating a loss of metallic character as seen in Li₂OH. (author)