This clinical study was conducted to evaluate and compare the post-operative pain after the using of two different irrigation tips: end-vented NaviTip tip and double sideport NaviTip irrigator tip immediate postoperatively and 4, 12, 24, 48 , 72 hours and 7 days utilizing Numerical rating scale (NRS(38 patients with vital lower posterior teeth without periapical radiolucency underwent one-visit root canal treatment, Root canals were prepared using NiTi ProTaper Universal rotary system then randomized into two equal gropus according to the needle used for irrigation group(A) NaviTip® 29-gauge 27 mm with End vented Tip and Group (B) NaviTip® 31-gauge 27 mm with Side vented Irrigator Tip , The needles of irrigation were penetrated 2 mm shorter than the working length. The trial design of this study is a Parallel randomized controlled trial. All demographic data, clinical and radiographic findings and modified NRS scores obtained from patients were statistically analyzed. Results showed that there was no statistically difference between the two groups regarding the demographic data, prevalence of pre-operative pain, after4 hours, 12 hours, 24 hours, 48 hours and 7 days. And number of Ibuprofen pills intake between both groups- Within the limitations of this study, it could be concluded that:There is no statistical significance difference between End vented NaviTip and Side vented NaviTip, while in both groups there was a statistically significant decrease in pain intensity preoperatively compared with all other time periods.