The infrared absorption spectra of triphenylphosphine oxide dissolved in CCl4 and n-hexane were recorded in standard liquid cells at room temperature. As a result of processing a number of spectra, the absolute integrated intensities were obtained for the fundamental, overtone and sum bands in the spectral region of 4500–170 cm−1. It was shown that the intensities of the fundamental bands practically do not depend on the solvent with the exception of the ν(P[dbnd]O) band. Our experimental findings are supported by quantum-mechanical calculations. The DFT calculations of the scaled harmonic frequencies and intensities with the wB97XD functional and def2TZVpp basis set showed the best agreement with the experimental values. The calculations allowed us to assign bands of 13C isotopologues and to qualitatively reproduce the behavior of the ν(P[dbnd]O) band upon solvent change.