ZnO varistor ceramics added a glass-frit 0.03 $wt\%$ were fabricated with variation of sintering temperature. The sintering temperature and time were $1125^{circ}C~1200^{circ}C$ and 2 h. The average grain sizes increased and the varistor voltage decreased with increasing the sintering temperature. The values of the specimen sintered at $1200^{circ}C$ were $23.7;{mu}m$ and 329 V, respectively. The leakage current of all specimens was less than $1;{mu}A$ at DC $82\%$ of varistor voltage. The clamping voltage ratio of the specimen sintered at $1175^{circ}C$ was 1.37. The endurance of surge current and the deviation of varistor voltage of the specimen sintered at $1175^{circ}C$ were 6400 $A/cm^2$ and ${Delta}-2.81\%$, respectively. After the High Temperature Load Test(HTLT) at $85^{circ}C$ for 1000 h, the specimen sintered at $1175^{circ}C$ showed the lowest deviation of varistor voltage of ${Delta}-1.92\%$.