Isothermal desorption kinetics at different temperatures of 1,2-dichloroethane (DCE) from syndiotactic polystyrene films have been studied by Fourier transform infrared spectroscopy. For beta-form films, where DCE is present only into the amorphous phase, nearly equal populations of trans and gauche conformers, during the whole desorption processes, are observed. On the other hand, for clathrate films, where DCE is present in both amorphous and crystalline phases, its trans conformer becomes largely predominant, as the desorption processes proceed. In agreement with previous FTIR and X-ray diffraction studies, these results can be rationalized by assuming that essentially only the DCE trans conformer is present in the clathrate phase. In this assumption, experimental desorption kinetics from clathrate samples can be separated into faster processes from the amorphous phase and slower processes from the crystalline phase. The validity of this separation procedure is confirmed by the close similarity between the desorption kinetics observed for the amorphous phase of beta-form films and calculated for the amorphous phase of clathrate films.