Volume resistivity, dielectric strength, dielectric constant, and loss tangent of unsaturated polyester resins and their GRP were studied as a function of the bromine content of the resin. The bromine was introduced by using bromostyrene as the crosslinking monomer. Bromine content was established by partial or total replacement of the styrene. Also, the effects of short and long water-boil treatments on these properties were investigated. The electrical and dielectrical properties were shown to be independent of the bromine content of the resin.