A study on the effect of the physical states of nitrogen on the breakdown properties of glass fiber reinforced epoxy was carried out. Surface breakdown and volume breakdown of glass fiber reinforced epoxy in nitrogen gas, cryogenic nitrogen gas and liquid nitrogen under AC voltages were investigated. In addition, breakdown strength-time to breakdown characteristics of glass fiber reinforced epoxy in these insulating media were also examined. The experimental data showed that surface breakdown strength and volume breakdown strength of glass fiber reinforced epoxy were significantly dependent on surrounding media, and similar results were obtained with breakdown strength-time to breakdown experiments. Glass fiber reinforced epoxy has the surface breakdown strength of 2.5 - 4.5 kV/mm, 8 - 16 kV/mm and 15 - 25 kV/mm when immersed in nitrogen gas, cryogenic nitrogen gas and liquid nitrogen, respectively. Similarly, the volume breakdown strength of glass fiber reinforced epoxy was determined to be about 48 kV/mm in nitrogen gas, 49 kV/mm in cryogenic nitrogen gas and 40 kV/mm in liquid nitrogen. For surface breakdown test, the lifetime index of glass fiber reinforced epoxy reached the highest value in nitrogen gas (55.6) and the lowest value in liquid nitrogen (43.5). For puncture breakdown test, glass fiber reinforced epoxy has the lifetime index of 47.6, 41.7 and 38.5 when immersed in nitrogen gas, cryogenic nitrogen gas and liquid nitrogen.