Epoxy resin is a material commonly used for the encapsulation of light-emitting diodes (LED). Three epoxy resins were chosen in this study: D.E.R.-331 was a bisphenol A type epoxy resin, Eporite-5630 was a bisphenol A type epoxy resin modified with a UV stabilizer, and ERL-4221 was a cyclo-aliphatic epoxy resin. The curing agent was methyl hexahydrophthalic anhydride (MHHPA), and the catalyst was tetra-butyl ammonium bromide (TBAB). Thermal, environmental, and optical properties of the cured epoxy resins were studied. It was found that cured ERL-4221 had better UV resistance, but other properties of ERL-4221 were lower because of the internal stress generated during the curing process. D.E.R.-331 showed better thermal stability, but the aromatic groups in the main chains caused sensitivity to photodegradation. Eporite-5630 had the advantages of D.E.R.-331 and better UV resistance than D.E.R.-331 because of the addition of UV stabilizer. Among the three materials, Eporite-5630 was the best choice of the balance properties for LED applications. This finding may assist in the selection of epoxy resins used in LED technology. (C) 2004 Wiley Periodicals, Inc.