Aim of the study:The purpose of the present study was to evaluate the sealing ability and adaptability of modified mineral trioxide aggregate (MM-MTA) in comparison to conventional mineral trioxide aggregate (Proroot MTA) by utilizing different retrograde cavity preparation techniques (conventional, ultrasonic and laser).Study design:One hundred and eleven maxillary incisor teeth were used in this study. The crowns were decapitated and the root canals were biomechanically prepared and obturated with gutta percha and resin sealer. Then the apical 3mm of each root was resected at 90o angle. The samples were divided into three main experimental groups; 30 roots each according to the method of root-end cavity preparation: end cavity preparation: Group I: Bur preparation. (B), Group II: Ultrasonic preparation. (US) , Group III: Laser preparation. (L).Each experimental group was further subdivided into two subgroups, 15 roots each one, according to root-end filling material that used: Subgroup (a): retrograde cavities filled with Proroot MTA, Subgroup (b): retrograde cavities filled with MTA capsule. Twenty one samples were used as controls; positive control (n=18) and negative control (n=3). Microleakage was assessed by immersing the samples in 0.2% Rhodamine B dye solution for the periods of 48 hours and one week.