Mica epoxy insulation as used for generator stator windings is required to be improved as regards withstand electrical stress and heat dissipation. Replacement of epoxy resins by epoxy nanocomposites is a useful method to fulfil a purpose of such improvement. This paper is aimed to evaluate PD-initiated breakdown (BD) performances as one of the most crucial characteristics using simulated model specimens. Two constituent materials, i.e. mica tapes and resin layers were set as about 40 and 10 μm in thickness, respectively. EDX analysis shows that the model specimens include silica nanofillers properly dispersed in narrow nanocomposite regions and are suitable for PD initiated BD experiments. It was found that PD initiated BD lifetime was 2.8 times in nanocomposites than in neat epoxy under a rather high electric stress condition.