The purposes of this study were to compare the bleaching efficacy of sodium perborate when mixed either with Superoxol or distilled water and to evaluate the efficacy of different location of intracoronal base on the presence of apical leakage of tested bleaching agents. Forty eight extracted human permanent incisors were stained via whole blood and canal fillings with conventional gutta percha were performed after routine biomechanical perparations. The experimental intracoronal base was placed either at the cementoenamel junction(group 3, 4) or 2mm below cementoenamel junction(group 1, 2). Walking bleaching was performed by two different combinations of bleaching agents : sodium perborate with distilled water in group 1, 3 and sodium perbrate with Superoxol in group 2, 4. The roots of the teeth were evaluated for the presence of color change to assess the leakage of bleaching agnets and the cervical one-thirds of the crown were evaluated for bleaching effect from the whiteness Indea calculated by spectrophotometer. The results were as follows : 1. At the end of 12 days, all the sample teeth demonstrated the increase of Whiteness Index at cervical 1/3 of crown although there were some minor differences among groups. 2. Regardless of location of the base, sodium perborate with superoxol)group 2, 4) showed better results in bleaching than the sodium perborate with distilled water(group 1, 3). 3. Bleaching agent leaked into the root area when the base was placed 2mm below cementoenamel junction but no leakage was found when the base was placed at the cementoenamel junction.