We report the first rotationally resolved observation of the infrared spectrum of the molecular complex C2H4–HCl. The complex was produced by a supersonic expansion through a pulsed slit jet. By means of a high-resolution tunable diode laser spectrometer, we have recorded the spectrum of the HCl stretching vibration for the isotopes C2H4–H35Cl and C2H4–H37Cl. From the analysis of the spectra, we determined the rotational constants and vibrational frequencies of both isotopes. These experimental results have been interpreted in view of obtaining information on the intermolecular interaction. The experimental data have been complemented by standard coupled cluster singles and doubles model including connected triple excitations with a correlation consistent polarized valence triple zeta basis set ab initio followed by grid calculations, in order to study the anharmonicity, the coupling between intramolecular and intermolecular motions, and the basis set superposition error effects. The results obtained in this study are compared to those of our previous work on the C2H2–HCl