Equilibrium nuclear configurations of the planar formaldehyde homodimer (H2CO)2 and the (H2CO)2…HF complex are determined in the MP2/6-311++G(3df, 3pd) approximation taking into account the superposition error of basis sets of monomers. Harmonic values of the frequencies and intensities of fundamental transitions between vibrational states of these hydrogen-bonded complexes were calculated using the Gaussian 09 package of programs. Anharmonic values of the frequencies and intensities of the ν(H–F) stretching vibration and several intermolecular vibrations in the (H2CO)2…HF trimer were obtained from variational solutions of one-, two-, and three-dimensional vibrational Schrödinger equations. The anharmonic influence of the C=O and hydrogen bond O…H–F stretching vibrations, as well as of librational vibrations of monomers, on the spectral parameters of the strongest ν(H–F) absorption band of trimer was studied. DOI: 10.1134/S0030400X17060042