This paper deals with experimental characterization of creepage discharge to improve the electrical characteristics of oil/pressboard (PB) composite insulation system by solid layer coating such as epoxy resin, and nano size silica/epoxy resin composite on PB surface under positive standard lightning impulse voltage (1.2/50 µs) using a needle/bar electrode arrangement in mineral oil. Creepage discharge properties of conventional PB are compared with solid layer coated PB, in terms of discharge final propagation length (ld) and partial discharge inception voltage (PDIV). As a result, it is found that partial discharge inception probability (Pd) of solid layer coated PB increases at all applied impulse voltage levels compared with that of conventional PB. The result is interpreted in terms of drying effect, surface modification effect and electron suppression effect by nano/epoxy composite coating on PB surface.