Biobased neat unsaturated polyester materials containing epoxidized methyl linseedate (EML) were processed with cobalt naphthenate as a promoter and 2-butanone peroxide as an initiator. Up to 25 wt % of the unsaturated polyester resin (UPE) was replaced by EML to process biobased UPE. The combination of UPE and EML resulted in an excellent combination for a new biobased thermoset polymer with a relatively high elastic modulus and a high glass transition temperature with the replacement of UPE with EML. Izod impact strength increased with increasing amount of EML. The Izod impact strength of the biobased UPE was correlated with failure surface morphologies observed by scanning electron microscopy.