Vibrational spectra of LaCrOS2 and LaCrOSe2 single crystals have been studied by far-infrared absorption and Raman scattering spectroscopy. Raman and infrared bands are analyzed according to the crystal structure which is built up by interconnection of CrOS5 octahedra with LaO3S6 polyhedra. Assignments of the Raman and infrared active modes are discussed in terms of vibrations of La-X and La-O bonds and octahedral CrOX5 groups (where X=S, Se).