Purpose: The purpose of this study was to evaluate the intensity and duration of postoperative pain after root canal preparation of primary maxillary molar teeth using two preparation techniques. Methods: A total of 110 patients requiring pulpectomy for asymptomatic primary molar teeth with non-vital pulps were included in the study. The patients were randomly assigned to two groups of 55 patients each, according to the canal preparation method used. In Group one, teeth were prepared up to size 35 with hand files. In Group two, teeth were prepared up to size 35 with Revo-S rotary instruments. Following canal preparation, teeth were obturated with zinc-oxide eugenol paste and then permanently restored. The presence of postoperative pain was assessed after six, 12, 24, 48, and 72 hours and after one week, using a four-point pain-intensity scale. Results: Except for those assessed after 72 hours and one week, patients who had their teeth prepared with hand files reported more intense postoperative pain than those who had their teeth prepared with Revo-S rotary files(P < 0.05). In both groups, postoperative pain decreased over time. Conclusions: Hand files caused more postoperative pain after pulpectomy in primary maxillary molar teeth compared to the rotary system.