Introduction: the aim of this study was to assess postoperative pain following application of 0.2% cetrimide gel intracanal medication as compared to calcium hydroxide paste in non-vital teeth with symptomatic apical periodontities utilizing a numerical rating scale (NRS). Participants and methods: Fourty-six patients diagnosed with a non-vital lower posterior teeth with symptomatic apical periodontities admitted to the department of endodontics, faculty of oral and dental medicine, Cairo University, Egypt, randomly divided into two equal groups. Chemomechanical preparation was performed using protaper universal rotary files and 2.6% sodium hypochlorite and 17% EDTA solution as irrigants. Canals were divided according to the intracanal medication applied into Cetrimide group using 0.2% Cetrimide gel (CTR) and calcium hydroxide (CH) group using CH pastethe. patients were instructed to report any painful sensation and mark his/ her level of pain on the numerical rating scale (NRS) after completion of the first visit. Results: showed no statistically significant difference, neither in intensity nor in incidence of pain at different follow up periods (after 4, 24, 48, and 72 hours and 4, 5, 6, and 7 days). After 1 week, CTR group recorded 87% of the cases were pain free compared to 100% in CH group. Both groups CTR and CH showed significant decrease in pain after 24 hours. There was no statistically significant difference between the two groups regarding placebo and analgesic intake. Conclusiion: There was no statistically significant difference between the two groups in postoperative pain intensity and incidence at follow up periods.