Aim: This clinical study was conducted to evaluate and compare the post-operative pain after the using of two different irrigation devices: EndoActivator and side vented NaviTip irrigator tip immediate postoperatively and after 4, 12, 24, 48, 72 hours and 7 days utilizing a numerical rating scale (NRS). The trial design of this study was a Parallel randomized controlled trial.Methods: Sixty patients suffering acute irreversible pulpitis in lower posterior teeth without periapical radiolucency underwent one-visit root canal treatment, Root canals were prepared using NiTi ProTaper Next rotary system then randomized into two equal groups according to the method used for final irrigation. Group (A) EndoActivator and Group (B) NaviTip® 31-gauge 27 mm with Sideport Irrigator Tip. The EndoActivator tip and the NaviTip were placed 2 mm shorter than the working length in all treated root canals. All demographic data, clinical and radiographic findings and NRS scores obtained from patients were statistically analyzed.Results: Results showed that there was no statistical significant difference between the two groups regarding the demographic data, prevalence of pre-operative pain. Also there was no statistical significant difference in postoperative pain reductionbetween the two groups. There was a statistical significant decrease in pain intensity starting 24 hours postoperatively compared to preoperative and 12 hours pain levels. There was no statistical significant difference regarding analgesic intake between the two groups.Conclusion: Within the limitations of this study it was concluded that both irrigation devices are reliable methods for irrigation having a normal range of postoperative pain.