A highly heat-conductive epoxy resin composition, which comprises epoxy resin in a liquid state at room temperature, a latent curing agent, a highly heat-conductive filler, and a non-ionic surfactant, where preferably the latent curing agent is mixed with a portion of the epoxy resin in a liquid state at room temperature to form a master batch, can keep a relatively low viscosity, even if a large amount of the filler is contained, and can be cured at a relatively low temperature for a short time, and has a distinguished storage stability as one-component composition.