Introduction: The aim of this study is to evaluate the prevalence of post-endodontic pain after single visit root canal treatment using manual versus rotary instrumentation technique on teeth with irreversible pulpitis. Method: Fifty patients suffering from irreversible pulpitis in maxillary first premolar with no evidence of apical periodontitis were divided into two groups. Group I: mechanical preparation was done using Revo-S system while group II: mechanical preparation was done using manual hybrid technique. The degree of post operative pain was measured by visual analogue scale (VAS) at 6, 12, and 24 hours after root canal treatment. Mann-Whitney U test was used to compare between the two groups, Wilcoxon signed-rank test was used to study the changes by time within each group, Chi-square (x2) test was used to compare between the two groups. Results showed that after 12 and 24 hours; Revo-S group showed statistically significantly lower mean VAS score than manual technique. Conclusions: Rotary instrumentation showed less postoperative pain after 12 and 24 hours than manual instrumentation technique.