Vibrational spectroscopy of size-selected formamide–water clusters, FA–(H₂O)_n, n = 1–4, prepared in a supersonic jet is performed with vacuum-ultraviolet–ionization detected–infrared predissociation spectroscopy (VUV-ID-IRPDS). The cluster structures are determined through comparisons of the observed IR spectra with theoretical calculations at the MP2/6-31++G** level. The FA–(H₂O)_n, n = 1–3, clusters have ring-type structures, where water molecules act as both single donor and single acceptor in the hydrogen-bond network between the amino and carbonyl groups of FA. For FA–(H₂O)₄, on the other hand, the absence of the free NH stretching vibration indicates formation of a double ring type structure, where two NH bonds of the amino group and the carbonyl oxygen of FA form hydrogen bonds with water molecules. An infrared spectrum of the formamide–water cluster cation, [FA–H₂O]⁺, is also observed with infrared predissociation spectroscopy of vacuum-ultraviolet-pumped ion (IRPDS-VUV-PI). No band is observed for the free OH stretches of neutral water. This shows [FA–H₂O]⁺ has such a structure that one of the hydrogen atoms of the water moiety is transferred to the carbonyl oxygen of FA⁺.