This study aims to evaluate the procedural errors of endodontic treatment that occurred during rotary mechanical instrumentation and root canal obturation process performed by dental students using NiTi rotary instruments. 258 out of 379 dental chart records and radiographic photographs that have completed endodontic treatment during 2014 and 2019 by using a rotary instrument, performed by undergraduate students at the College of Dental Medicine, Rangsit University were included. The digital periapical radiograph of pre-treatment and post-treatment were evaluated by setting criteria. The procedural errors were defined as void, underfill root canal filling material, overfill root canal filling material, ledge formation, perforation, fracture instrument, and miss canal. The sample included 83 anterior teeth and 175 posterior teeth (32%, and 68% respectively). The types of teeth consisted of 83 incisor and canine teeth (31.78%), 73 premolar teeth (28.29%), and 102 molar teeth (39.93%). The prevalence of overall procedural errors was 31.78%. In terms of the anterior position, there were 83 root canals. The prevalences of void detection, underfill root canal filling material, overfill root canal filling material, and ledge formation were 4.82%, 2.41%, 4.82%, and 7.23%, respectively. For the posterior position, there were 444 root canals. Posterior teeth exhibited prevalences of void detection, underfill root canal filling material, overfill root canal filling material, fracture instrument, perforation, and ledge formation were 9.46%, 4.05%, 3.15%, 1.13%, 1.58%, and 6.31%, respectively. There were no significant differences between tooth position and all procedural errors. The overall procedural error rate of endodontic treatment performed by undergraduate students using rotary instruments was 31.78%. Most of the cases occurred during the root canal obturation process. These present data of procedural errors could be a benefit for improving both pre-clinical and clinical curriculum, as well as endodontic skills of undergraduate students.