Objective: To evaluate the auto apical reverse motion of Tri Auto ZX at working length determined by Dentaport Root ZX. Study design: Cross-sectional design. Place and duration of study: Department of Operative Dentistry, Islamic International Dental College, and the duration of study was 6 months. Materials and methods: Total 72 extracted teeth were used in the present study and standard access cavities were prepared in all the teeth. For in vitro working of Dentaport Root ZX and Tri Auto ZX an apparatus was designed which used normal saline as the conducting medium to ensure free movement of ions between electrodes of electronic apex locator (EAL). Working length was measured electronically using Dentaport Root ZX and noted as Electronic length (EL). The canals were then prepared using Protpaer files till F2 using Tri Auto ZX and the length at which it starts auto apical revere motion (AAR) was noted as AAR. Results: EL showed a mean of 14.69 ± 1.137 mm and SD of 1.137. Measurement at which Tri Auto ZX started its AAR motion showed that the minimum length of canal was 12.5 mm and maximum length was 17.5 mm with a mean of 14.687 ± 1.089 and SD of 1.087. The difference of root canal length measurements taken by EL and AAR motion of Tri Auto ZX showed a minimum difference of -1.5 mm and a maximum of 1 mm with mean difference of -0.014 ± 0.4819 mm. Out of 72 extracted teeth that were used in the present study the difference between EL and AAR was insignificant (p<0.05). Conclusion: In this study it was also established that not only Root ZX is capable of correct determination of the working length but its canal preparation module i.e. Tri Auto ZX is also capable of preparing the canal at the length determined by Root ZX.