Aim: A randomized clinical trial was used to assess and compare the effect of calcium hydroxide/ nanosilver particulate combination intracanal medicament versus calcium hydroxide intra canal medicament on postoperative pain in symptomatic root canal treatment failure cases.Methods: Forty participants diagnosed with symptomatic root canal treatment failure in maxillary and mandibular anterior and premolar teeth were randomly assigned into two equal groups, according to intracanal medication used, either combined calcium hydroxide silver nanoparticulate or calcium hydroxide with distilled water.Root canal retreatment performed in two visits, first visit was removal of old coronal restoration, rubber dam application, removal of old gutta percha from canal by protaper universal retreatment files, working length determination by apex locator and confirmed by radiograph, chemo-mechanical preparation with protaper universal rotary system and 2.5 % NaOCl irrigation with 19% EDTA gel as lubricant; application of intracanal medication as randomly assigned. Then second visit after one week, access opened and medication removed by aids of 5ml saline , 20% citric acid and 5ml again saline as final irrigant, obturation was done with lateral condensation technique with a resin sealer. Pain was assessed pre-operatively, then after 6, 12, 24 and 48 hours post operatively. The participants ranked their postoperative pain level at selected periods on a NRS scale (no, mild, moderate, and severe). All demographic data and NRS scores were collected from the patients and statistically analyzed.Results revealed that: 1.There were no statistically significant differences in postoperative pain between the two groups as regards age range, gender, tooth type, tooth location and number of canal/s. 2. There was no statistically significant difference between the two groups in postoperative pain intensity and incidence at the different paincategories at 6, 12, 24, 48 hours. But there was statistically significant decrease in median NRS scores for all time periods postoperatively in each group compared with preoperatively. Moreover, all other time periods (6, 12, 24, 48 hours) were statistically significant from each other in each group.Conclusions: it could be concluded that: Calcium hydroxide silver nanoparticulate combinations group (Group A) is effective intracanal medicament in symptomatic endodontic retreatment cases as it decrease postoperative pain by time especially after 6 hours (95%).