Sunflower oil (SO) is a renewable resource that can be epoxidized, and the epoxidized SO has potential uses as an environmentally friendly in polymeric formulations, especially for poly (vinyl chloride) (PVC). Epoxidized sunflower oil (ESO) was prepared by treating the oil with peracetic acid generated in situ by reacting glacial acetic acid with hydrogen peroxide. Epoxidation was confirmed using spectroscopic and titration methods. ESO was used as a coplasticizer in PVC for the partial replacement of di-(2-ethyl hexyl) phthalate (DEHP). The effect of ESO on the thermal stability of plasticized PVC was evaluated by using synmero scale for the sheets. In presence of ESO plasticized PVC samples showed a reduction in discoloration and the number of conjugated double bonds. By using thermogravimetry, the incorporation of 15/45 of ESO/DEHP in PVC presents the lowest weight loss. The results of the shore hardness and mechanical properties showed that a proportion of DEHP could be substituted by ESO. By use of DMA, the formulation which contains 25 % wt of ESO in plasticizer system shifts the glass transition temperature (T-g) to ambient temperature. The migration phenomenon was studied on PVC based samples plasticized with DEHP and ESO in varying amounts. The migration was monitored by the weight loss percentage of the samples immersed into n-hexane or heated in an oven. The amount of extracted or volatilized DEHP is proportional to the added ratio of ESO in plasticizer system. All of this favored the partial replacement of DEHP by ESO as biobased plasticizer for flexible PVC. (C) 2010 Wiley Periodicals, Inc. I Appl Polym Sci 118: 3499-3508, 2010