Background: Recurrent aphthous stomatitis (RAS) is a common oral disease. Sagi is one of the natural remedies of traditional Persian medicine that has been used as an antiseptic mouthwash. We designed a randomized, placebo controlled clinical trial to evaluate the efficacy of Sagi in management of RAS. Material and Methods: In this randomized, double arm, double blind, placebo-controlled clinical trial, 26 patients received Sagi mouthwash as intervention group and 26 patients received placebo as the control group for four consecutive days. Primary outcome measure the pain severity of lesions assessed by visual analogue scale (VAS). The size of the aphthous lesions as another outcome was also measured via millimeter paper. Results: Regarding within-group changes, a significant decrease was observed in the scores of pain in both group of the study (p<0.05). Moreover, a significant decrease was observed in the size of lesions in Sagi group (p=0.003). However, no such change was seen in the placebo group (p=0.075) (Table 2). According to independent sample t test, there was a significant difference in the mean change of pain score over the study period in the Sagigroup compared with the placebo group (p=0.004). Conclusion: According to the results of this study, it seems that Sagimouthwash could improve the symptoms of RAS compared to placebo.