Objective: This study was designed to compare two rotary instruments: WaveOne and ProTaper Universal in regard to centering ability when shaping simulated canals. Materials and methods: This is an in vitro study in which we used 20 curved L-shaped simulated canals in plastic blocks (EndoTraining Bloc-L, Dentsply-Maillerfer, Ballaigues, Switzerland) which were standardized in length, taper and curvature.