Low-voltage ZnO-based varistors were made by seed grain method at various sintering conditions. Their microstructure and electrical properties were investigated and comlpared with those of the ZnO varistors made by a conventional method at the same sintering condition. During the sintering process, the added seed ZnO grain rapidly grew to be a gaint grain(above 500$mu extrm{m}$) provinding easy current path. Therefore the breakdown voltage was lowered as much as the order of 1/10-1/5 in comparison to that of the varistor made by a conventional method. But the grain size of the giant ZnO was little influenced by sintering condition, so the breakdown voltate was also little influenced. The weight loss was decreased by the addition of the seed grain, because the giant grain decreased the evaporation area. Therefore the nonobmic property of the specimen made by seed grain method was little influencedby sintering condition. In this research the low-voltage varistor made by seed grain method showed the least leakage current when sintered at 1150$^{circ}C$ for zero hour.