Glass powder reinforced epoxy was used in the fields of plastic sealing of semiconductor devices. In such environment, the materials were exposed in the high temperature, and the visco-elastic behavior must occur in the materials. However, there are few reports about these materials focused on visco-elasticity. Therefore, the analysis of visco-elastic behavior was an important issue to be taken in account. In this study, the stress relaxation behavior and dynamic mechanical analysis of epoxy composites filled with different amounts of glass powder were investigated. On the dynamic mechanical analysis, the glass transition temperature decreased with the increment of the amount of glass powder contents. And the viscosity at high temperature also decreased when the contents were augmented. On the stress relaxation test, master curves of stress relaxation were obtained, and the time-temperature superposition principles was ascertained. The slopes of time-temperature shift factors were changed depending on the amount of glass powder. Therefore, the time-temperature shift factors were calculated by using the relationship between the slopes of the time-temperature shift factors and the amounts of glass powder. The effect of amounts of glass powder on stress relaxation was also investigated. When the amount of glass powder increased, then the stress relaxation curves shifted to short time side. Comparing the master curves of stress relaxation with the different amount of glass powder, it is understood that the stress relaxation behavior of each material is similar. The effect of glass powder contents on stress relaxation behavior showing the effect of reinforcement and heat resistance is also discussed.