Background <p>This study aimed to evaluate the influence of the operator’s experience on shaping ability with single-file Nickel-Titanium systems.</p> Methods <p>The One Curve (OC) rotary file system and the One RECI (OR) reciprocating file system, both with a tip size of #25/0.06, were used by four inexperienced clinicians (IOC and IOR) and four endodontists (EOC and EOR) to shape endo-training blocks with J-shaped simulated canals. Each operator prepared 5 canals per system, giving 20 canals per group. Pre- and post-operative images of simulated canals were superimposed. The total amount of straightening and the change in the radius of curvature and centering ratios were determined. The results were analyzed using two-way analysis of variance, with operator experience and file system as fixed factors, followed by Tukey’s post hoc comparison at a significance level of 95%.</p> Results <p>The One RECI system produced significantly greater overall straightening than the One Curve system (<i>p</i> = 0.016), while operator experience had no significant effect on straightening or on the change in the radius of curvature (<i>p</i> &gt; 0.05). Operators experience significantly affected the centering ratio from the apical third to the center of the curvature (<i>p</i> &lt; 0.05), with inexperienced operators generally achieving higher centering ratios, except near the center of curvature. No effect of experience was found at the apical terminus or in the coronal, straight portion of the canal (<i>p</i> &gt; 0.05). Inexperienced operators using the One RECI system achieved significantly higher centering ratios than all other groups in the apical third (<i>p</i> &lt; 0.05). No significant experience × system interaction was found for any parameter.</p> Conclusion <p>Within the limitations of the present study, shaping outcomes with single-file NiTi systems were influenced by both operator experience and instrument kinematics, although no significant interaction between these factors was detected.</p>