This work is aimed at studying the plasticizing effectiveness of bio-plasticizers for soft PVC obtained from cardanol. Cardanol is a by-product of cashew industry, and represents a sustainable, low cost and largely available natural resource. The chemical structure of Cardanol is similar to that of pentadecyl phenol, with some degree of unsaturation on the side chain. In order to increase the compatibility with PVC, cardanol was subjected to a chemical modification, including acetylation of the hydroxyl group, followed by epoxidation of the side chain double bonds. In the view to optimize this latter chemical procedure, different types of epoxidized cardanol-based plasticizers were produced, characterized by different yields of the epoxidation reaction. The so called “PVC gelation” was measured by rheological analysis, which provides the evolution of viscosity during heating of the PVC plastisol, i.e. a suspension of PVC powder in the low viscosity plasticizer. The most relevant parameters used to quantify the plasticizing effectiveness, are the onset temperature of gelation, the maximum viscosity and the rate of plasticizer absorption. Lower gelation onset temperature, higher maximum viscosity and faster absorption were attained for the plasticizers characterized by the higher yield of epoxidation. These observations suggested a better plasticizing effectiveness of the products characterized by the higher yield of epoxidation. The durability properties were also measured by plasticizer desorption tests carried out at 105°C. The coefficient of diffusion, obtained by power law fitting of the weight loss of soft PVC as a function of time, was found to decrease with increasing yield of epoxidation. This indicates that an improved durability of soft PVC can be obtained by improving the conversion of cardanol double bonds to epoxies. For the plasticizers characterized by the higher yield of epoxidation, furthermore, the coefficient of diffusion was found to be lower t