The purpose of this electrochemical study was to determine and compare the sealing effect of three commonly used calcium hydroxide-based sealers (Sealapex, Apexit, and CRCS) with that of Roth 801 which is a ZOE-based sealer. 64 single rooted teeth were used in this experiment. After removing the crown, the teeth were devided into 4 groups of 15 in each and obturated with gutta-percha and experimental sealers. 4 teeth were as controls(2 positive and 2 negative). The results were as follows : 1. During the observation period, all sealers showed varying degree of microleakage. 2. The mean leakage currents according to the electrochemical study of each group showed $0.418{pm}0.006mV$ for Roth 801, $2.03{pm}0.035mV$ for Sealapex, $3.33{pm}0.069mV$ for Apxit and $6.48{pm}0.097mV$ for CRCS group. The positive control group showed 600mV. 3. There were statistically significant difference in mean leakage among experimental groups. ZOE-typed Roth 801 sealer was the lowest, and Sealapex, Apexit, CRCS group in that order showed increased leakage(P<0.05). 4. Roth 801, Sealapex and Apexit group showed increasing leakage with time, but CRCS group showed stable or decreasing leakage tendency.