The manufacture of polymer composites through resin transfer molding (RTM) precoess involves the impregnation of fibrous resinforcements in a mold cavity and the subsequent cure reaction of a reactive polymeric resin. Curing stagge involves hea t transfer coupled with thermoset resin cure. In this study an energy balance was set jp including the bulk properties of composites, which were dependent on temperature, degree of cure and fiber volume fraction. A full three-dimensional finite element method was used for solving the heat transfer problem of plate geometry. We developed a computer program capable of predicting the temperature profile and the degree of cure in a mold as a function of cure conditions and sample geometry. For a polyester/glass fiber composite, the temperature and the degree of cure distribution inside a three-dimensional flat plate could be predicted. Through numerical simulations it was shown that the appropriate selection of cure cycle was the most critical processing parameter in the given material system.