The author has studied comparatively the sealing quality of conventional Z.O.E. cement, Kerr sealer and Nogenol sealer by means of penetration of 2% methylene blue solution through the root apex of human teeth in 72 cases as time elapsed. The results were as follows; 1. All the specimens, whose dye immersion time is two days, showed dye penetration of low degree unrelated to the kinds of root canal sealer. 2. Kerr sealer group, like conventional Z.O.E. group, showed dye penetration of high degree related to increased time of immersion in the dye. 3. In Nogenol group, there was slight increase in penetration related to increased time of immersion in the dye. 4. Kerr sealer group showed comparatively lower grade of dye penetration than conventional Z.O.E. and higher than Nogenel sealer.