The surface discharge along the interface of solid-liquid insulation is one of the main causes of the deterioration of the life of a power transformer. This experimental study investigates the effects of different solid and liquid insulation materials on the surface partial discharge (PD) characteristics. The liquid insulation materials utilized are mineral oil and synthetic ester, whereas the solid insulation materials are cellulose board and Nomex board. The surface PD characteristics in various combinations of solid and liquid insulation materials are investigated using PD inception voltages (PDIV), apparent charges (pC), and phase-resolved PD (PRPD) patterns, and the comparative analysis is presented. Moreover, topography and composition of samples during surface discharges phenomena have been discussed using high-resolution images and chemical composition obtained using the scanning electron microscope (SEM) and energy dispersive spectroscopy (EDAX). The findings of this article will assist in understanding the behavior of surface PDs under various conditions. © 1973-2012 IEEE.