Highly fire retardant unsaturated polyester resins which exhibit low burning rates, low smoke generation and beneficial char formation in the presence of a flame are provided by incorporating up to about 5 weight percent of copper or a copper compound in a halogen containing unsaturated polyester of a polycarboxylic compound and a polyhydric alcohol having greater than about 4 weight percent halogen based on the weight of unsaturated polyester resin and a copolymerizable unsaturated monomer. The unsaturated polyester resins are copolymerized with an unsaturated monomer for use in castings, laminated products and other reinforced articles.