Plasticizer migration from flexible poly(vinyl chloride) comprises an important aspect, especially when packaging foodstuffs and pharmaceuticals. Much of the published work has been intended either to correlate migration into simulants with that into foods or to study migration into simpler extractants, enabling the various parameters involved in migration to be studied in isolation. According to the latter approach, the migration of dioctyl phthalate into petroleum oils has been studied already in our laboratory and in this paper results are presented in an attempt to reduce or prevent migration by u.v. irradiation. The effect of irradiation time on short and long-term migration behavior was examined together with the influence of the immersion temperature. The nature of the liquid environment seemed to be a predominant aspect: high viscosity oils presented a satisfactory behavior in contrast with those of lower viscosity in which the prevention effect was rather negligible. On the other hand, primary kinetics studies yielded similar results with those already established for untreated material (i.e., good conformity to the short time Fickian approximation).