Abstract Bio‐based thermosets based on vegetable oils are promissory materials due to their good performance, renewability and biodegradability. In this work, accelerated weathering tests were performed over bio‐based thermosets obtained from castor oil to evaluate the long‐term performance under environmental conditions. The thermosets were obtained through homopolymerization or copolymerization with styrene of maleated castor oil methacrylate. The changes in chemical and physical properties were monitored by Fourier‐transform infrared spectroscopy (FTIR), color measurements, scanning electron microscopy (SEM) and proton nuclear magnetic resonance ( 1 HNMR). Both materials showed evidences of chemical changes, such as formation of double bonds and hydroxyl groups, as well as the decomposition of carbonyl ester groups. The observed physical changes were discoloration as well as the formation of cracks and blistering. However, the degradation phenomena were less severe in the copolymer due to the high stability of styrene moieties.