This study focused on the experimental and theoretical evaluation of the thermal stability of epoxy resins for the development of neon transformer housings. A variety of hardeners was added to the epoxy resin to improve the thermal stability and workability of the neon transformer. Silicon dioxide (SiO2) also was added as a reinforcement filler. Then, the variation of the viscosity and thermal stability with the amount of reinforcement filler and hardener was evaluated. A hardener modified with cycloaliphatic aminewas superior to the polyamide type hardener in terms of the physical properties and the optimum curing conditions were found to be a curing time of 70 min at 343 K. The viscosity of the epoxy resin increased with increasing amount of silicon dioxid(SiO2), whereas the volume deformation ratio used for the evaluation of the thermal stability decreased. As a result, it was concluded that the polyamide type hardener had superior characteristics in terms of the workability and thermal stability and that the optimum silicon dioxide (SiO2) content was 50 wt%.