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To understand the space charge formation of nano-sized magnesium oxide (MgO)/low-density polyethylene (LDPE) nanocomposite materials, the space charge up to the breakdown has been investigated under DC increasing ramp field. A negative charge was dominated in 0 phr sample. A positive charge was dominated in nano-composite sample. The field increment (= the maximum field - the average field) of 0 phr increased with increasing average field and then was saturated with a few rises and falls before the breakdown. In case of 1 phr sample, after showing the peak the field increment turned to decrease with further increase of the average field. In case of 2 phr and more, the clear decrease of the field increment was not observed due to a few positive charges. The space charge distributions of 1 phr shows different distribution between 1 st and 2 nd filed applications while that of 0 phr did not. From these results, it was considered that the homo space charge effect at the anode brought by charge trapping effect of MgO nano-filler controlled the space charge formation in nano-composite.