Visible-light-cured (VLC) composite resins have been widely accepted in dental clinics because of their aesthetic merit and ease in handling [1]. Visible light (VL) irradiation of composite resins at intraoral temperature is, however, said to be insufficient for maximum polymerization, leading to wear and discoloration problems [2-4]. To offset these drawbacks, a method for post-curing by heat has been introduced. These composites are now used as V L C inlay composite resins [5]. For the purpose of providing VLC inlay composite resins with improved clinical performances, it seems necessary to study the monomer mixture suitable for both VL and heat curing. Bisphenol A glycidyl dimethacrylate (bis-GMA) has been proven to be a useful base monomer for various dental composite resins [6]. Due to its high viscosity, however, bis-GMA has to be added with diluent monomers to render the handling and incorporation of filler easier [7]. Although some attempts have been made to examine the influence of diluent monomers on the curing behaviour of bis-GMA based binary monomer mixtures [8], such effects are still not well clarified. Therefore, the objectives of this study were, firstly, to prepare four bis-GMA based binary monomer mixtures and evaluate their curing performance by VL and by VL plus heat with residual monomer measurements and mechanical strength (diametral tensile strength) measurements and, secondly, to assess the effects of post-curing by heat on the properties of the once photo-cured copolymers. Table I shows the formulation of four bis-GMA (D-GMA, Shin Nakamura Co., Japan; lot no. 1105K) based binary monomer mixtures, in which one of the following four monomers was used as the diluent monomer: triethyleneglycol dimethacrylate