The effect of temperature on creepage discharge and pressboard (PB) puncture occurring at the rapeseed or mineral oil/pressboard interface was investigated under alternating current (AC) voltages. The experiments were performed using the pseudo-composite insulating system (PCIS) which is consisting of the pressboard, tungsten needle electrode, counter electrode and back side electrode immersed in the test oil with different temperatures in ranging −5 °C to 95 °C. The discharge shape, streamer final length, discharge current, light signal, optical spectra, PB puncture and PB surface damage were observed under different voltages applied to the needle electrode. A particularly noteworthy result is that at oil temperatures above 75 °C, the initial discharge that occurs at a given voltage is very intense compared to other low temperatures, but the progression of creepage discharge is suppressed and PB puncture occurs quickly without the discharge reaching the counter electrode. From this, it can be understood that creepage discharge accidents in oil-pressboard insulation systems are very likely to occur at high temperatures