In previous studies (Shikwa Gakuho 80: 473-485, 1471-1486, 1980), the authors have reported on sealing properties in vitro. But the recent development of many new sealers makes necessary a detailed reexamination at this time. The experimental materials were as follows; Zinc oxide eugenol sealer......Canals Calcium hydroxide eugenol sealer......CRCS, Dentalis KEZ Calcium hydroxide guaiacol sealer......FR Hydroxyapatite sealer......Finapec APC, Apatite root sealer TYPE III The experimental procedure employing a glass tube and the dye-penetration method was similar to the one used in previous studies. Results of the investigation; 1. Degrees of dye penetration were classified into 3 types i) Immediate penetration through the zone between the material and the glass tube within 2 days.--Apatite root sealer TYPE III, Dentalis KEZ ii) Little penetration within 12 hours but gradual penetration to the deep zone thereafter.--CRCS, Canals iii) Slight penetration within 7 days and then gradual penetration 1/5 of the way through the zone between the material and the glass tube.--Finapec APC 2. Dye penetrated through the material in the case of apatite root sealer TYPE III and FR.