Abstract: Based on the self-developed nanosecond pulsed test platform with output voltage of 30 ns risetime and 100 ns half width, and the standard dielectric strength DC tester, the breakdown characteristics of four liquid dielectrics (transformer oil, glycerol, deionized water and Galden HT200) under DC and nanosecond pulses were experimentally studied and compared. The following conclusions were obtained: (1)Under both DC and nanosecond pulse, Galden HT200 has the highest breakdown field strength which is more than 40% higher than that of the transformer oil. (2) Under the nanosecond pulse, the breakdown field strength of Galden HT200 and transformer oil both increased by 6.5-7 times than those under DC. And it took the shortest time(nanosecond scale) for Galden HT200 to breakdown, followed by the transformer oil(20 ns), then glycerol(45 ns) and deionized water(70 ns). (3) After multiple breakdowns, a lot of carbonized discharge products were accumulated at the electrode gap in the glycerol which has the largest viscosity coefficient. However, there are no obvious breakdown traces in the Galden HT200 and deionized water, which both have the smaller viscosity coefficient. But obvious shock waves were observed in the Galden HT200 and deionized water, which make the gap electrodes  loose.