This randomized clinical trial evaluated and compared the post-operative pain after using two different irrigation tips; end-vented NaviTip tip and double side-vented NaviTip irrigator tip immediate postoperatively and 4, 12, 24, 48, 72 hours and 7 days with irreversible pulpitis in mandibular posterior teeth. Participants and methods: 38 patients aged between 18-60 years were included in the study and underwent one-visit root canal treatment. Root canals were prepared using NiTi ProTaper Universal rotary system, then participants were randomized into two equal groups according to the needle used for irrigation: Group (A) NaviTip 29-gauge 27 mm with End vented Tip(control) and Group (B) NaviTip 31-gauge 27 mm with Side vented Irrigator Tip(intervention), The needles of irrigation were penetrated 2 mm shorter from the working length. Postoperative pain was recorded using numerical rating scale (NRS) and at different follow up periods as previously mentioned. The intake of the given placebo capsules and prescribed analgesic tablets were recorded. Results: there was no statistically difference between the two groups regarding the demographic data, prevalence of pre-operative pain and postoperative pain at 4 hours, 12 hours, 24 hours, 48 hours and 7 days(P>0.5). There was no statistically difference between two groups regarding placebo and analgesic tablets intake(P>0.5). Conclusion: Based on these findings, it could be hypothesized that there is no significance difference between End vented NaviTip and Side vented NaviTip and between numbers of analgesics pills intake between two groups. There was significant decrease in pain intensity preoperatively compared with all other time periods.