Background. Recurrent aphthous stomatitis (RAS) is a common oral lesion with unknown etiology. Several treatment strategies are introduced for the treatment of RAS. In this regard, the therapeutic effects of Rhus coriaria, as one of the potential treatments, have recently caught attention. Since the clinical efficacy of Rhus coriaria has not been examined adequately. This study aims at evaluating the therapeutic effects of Rhus coriaria among patients with RAS. Methods. Twenty-two patients with RAS were divided into two groups (
n
=
11
). The experimental group received three pills of Rhus coriaria daily for 6 days, while the control group received triamcinolone (oral paste) three times a day for 6 days. The pain and size of the lesion were measured on the 1st, 2nd, 3rd, 4th, 5th, and 6th days. The data were analyzed by SPSS 16. In this regard, Student’s
t
-test and Sidak pairwise tests were used for assessment of inter and intragroup comparisons of the pain and the size of the lesion, respectively. Results. Intergroup comparisons indicate that there is no difference between the experimental and the control group (
p
>
0.05
). Whereas, the intragroup analysis of the pain revealed significant changes (
p
<
0.05
) in most of the time points for both groups. Besides, the intragroup analysis of the lesion size, showed significant changes in all the time points in the experimental group (
p
<
0.05
). The results in the control group exhibited the same pattern, except on 1-5, 1-6, 2-6, and 3-6 intervals in the control group. Conclusions. The application of Rhus coriaria could significantly reduce lesion size and pain in patients with RAS. Accordingly, Rhus coriaria can be an effective medication for RAS treatment.