New composites from unsaturated polyesters (Ups), with high 'green' content, and fly ashes (FA) were studied for the first time. All the monomers used in the synthesis (fumaric acid, succinic acid, propylene glycol, 1,3-propanediol) can be obtained from renewable resources, with the exception of diethylene glycol. The composites were prepared by crosslinking the UPs in the presence of FA, using styrene (St), methyl methacrylate (MMA) and a mixture of acrylated epoxidized soybean oil (AESO) with St as reactive solvents. The results showed that the incorporation of the FA improved the thermal stability of the composites. Regarding the thermomechanical properties, it was found that the incorporation of 50% (w/w) FA led to composites with higher elastic modulus (E') and higher glass transition temperature (T-g) than the neat polymeric matrix. These observations indicate a good compatibility between the FA and the polymeric matrix. (C) 2016 Elsevier B.V. All rights reserved.