The miniemulsion polymerization has been extensively used for nanocapsules formation by incorporating high concentrations of costabilizer or other hydrophobic liquid. The encapsulation of hydrophobic liquids may affect the kinetic mechanisms involved in the polymerization. In this study, miniemulsion polymerization reactions of MMA were conducted with encapsulation of vegetable oils, using different types (linseed and andiroba oil) and amounts of oils. It was observed a decrease in the reaction rate that was proportional to the number of double bonds present in the oil. Polymers with lower molecular weights were obtained when oils with higher number of double bonds were used. A mathematical model was developed to represent the kinetics of these reactions, including all the other kinetic mechanisms associated to free radical miniemulsion polymerization. The model was able to predict the variation in the polymerization reaction rate depending on the type and amount of the vegetable oil.