Optimized quantity of nano-aluminium (Al) filler mixed with epoxy resin using percolation threshold criteria was adopted to fabricate nanocomposite to achieve its desired space-charge and charge-trap properties. The variation in Surface potential of nanocomposites due to accumulation of charge on to the insulating material under transient voltages was investigated. Threshold electric field of the composites was measured using pulsed electro-acoustic technique which captures the variation in space-charge density and correlated it with beneficial effect of mixing nano filler in to epoxy resin.