The aim of this in vitro study was to compare the shaping characteristics of two types of nickel-titanium endodontic file systems with regard to the following parameters: Canal straightening, Canal deviation and Instrumentation time. Fifty severely curved canals simulated in resin blocks were prepared to an apical size 25 using Protaper Universal orNeolix systems (n=25 canals/group). The angle of canal curvature was determined before and after instrumentation. Pre- and post-operative images were superimposed to determine any canal deviation. The instrumentation time was also recorded. The data were statistically analyzed by using independent sample t-test and the Mann-Whitney U-test. There were no significant differences between the groups in terms of the change in canal angle (P > 0.05). The Neolix system produced less canal deviation at 7 of the 12 measuring points (p<0.05). The Neolix system also required less instrumentation time (p<0.05). Both rotary systems were capable of maintaining the original curvature of the root canal; however, the Neolix system resulted in less canal deviation as well as shorter instrumentation time.