Root canal treatment is the removal of vital or necrotic pulp from the canal system of an infected tooth followed by replacement with an inert filling material.Traditionally,  root canal treatment  was performed in multiple visits, with medication between root canal preparation and obturation, which  aims to reduce or eliminate microorganisms and their by-products  before obturation.In recent times, there is a growing concern about the  multiple appointments as there is  no significant differences in antimicrobial efficacies have been reported between the single- and multiple-visit treatments . Furthermore, the recent invention of rotary  systems and improvements in the irrigation  delivery systems have facilitated the  better  instrumentation and disinfection of the root canal,  which inturn  makes the single-appointment treatment more convenient than before  along with other advantages like timesaving, better patient acceptance, and reduction of the interappointment infection risks,  reduced flare-ups (Walton & Fouad 1992, Imura & Zuolo 1995, Albashaireh & Alnegrish 1998). However the argument for single-visit treatment  still relies heavily on microbial eradication,postoperative pain, healing rate.  Numerous studies evaluated the effectiveness and post treatment pain of single- versus multiple-appointment root canal treatment and reported no significant difference in effectiveness (healing rates) and postoperative pain between these 2 treatment regimens. Sathorn et al conducted a metaanalysis in which he gave the conclusion that single-visit root canal treatment appeared to be slightly more effective than multiple visit, i.e. 6.3% higher healing rate.The aim of the present randomized controlled clinical trial is to evaluate the post-operative pain in patients underwent single visit root canal treatment with Mtwo and Protaper next rotary systems.