Objectives. The aim of the present study was to compare postoperative pain on using 1.3% and 5.25% sodium hypochlorite irrigating solutions utilizing the visual analogue scale. . Material and methods: Sodium hypochlorite solutions are recommended as the main irrigants. This is because of their broad antimicrobial spectrum as well as their unique capacity to dissolve necrotic tissue remnants. Root canal treatment was completed in two visits, root canal preparation was done using NiTi protaper rotary system. Working length was estimated by using apex locator, then confirmed with an intraoral periapical radiograph. Irrigation was done with 27- gauge needle. The root canals were obturated with gutta-percha and resin sealer using lateral compaction technique. The patient was engaged to report the pain on visual analogue scale before treatment, immediately after cleaning and shaping, after 3, 24, 48 hours, 7days and immediately after obturation. Results: There was no statistically significant difference in mean of VAS for NaOCl 5.25% and 1.3% before treatment, immediately after treatment and at 7 days. However, there was a statistically significant difference between the two groups at 3 hours, 24 hours, 48 hours and at Post-obturation period where, 1.3% NaOCl showed statistically significant lower mean VAS than 5.25% NaOCl. Conclusions: The use of lower concentration of NaOCl (1.3%) irrigation solution can result in a significant reduction of postoperative pain levels in comparison to higher concentration of NaOCl (5.25%). The highest intensity of pain occurs at 3 hours post operatively.After 3 hours the intensity of pain decreases gradually.