Objective: the aim of this study was to assess and compare in vitro; the sealing ability and adhesiveness of realseal resin endodontic obturation system in oval and round root canals using system B obturation. A total of 58 extracted human teeth were selected for this study. The canal shape was determined using periapical radiograph of each tooth in buccolingual and misodistal directions. Teeth were divided into two equal groups: Group1: 29 mandibular incisors were used with oval canal where the long: short diameter is > 2 at 5 mm from the apex. Group2: another 29 mandibular premolar were used with round canal where the long: short diameter is= 1. All root were instrumented. Decoronated the obturated using system B obturation technique for sealing ability, 14 teeth from each group were subdivided into 10 teeth for experimental group and 2 teeth for positive control group and 2 teeth for the negative control group. Teeth were placed in methylene blue dye, lngitudinually sectioned the coronal and apical dye penetration were measured. For adhesiveness, ten teeth from each group were cross sectioned at 5.7 and 11 mm from the apex. The sections were submitted for measuring micropuch- out bond strength. 5 specimen from each group were examined using environment scanning electron microscope (ESEM) for marginal adaptation. The results of this study showed no statistically significant difference between round and oval canal of either coronal or apical dye penetration.