BACKGROUND: Rheum ribes L. is a plant native to China, Iran, Turkey, India, and a few other countries. Antidiarrheal activity is considered to be one of its important properties according to various systems of traditional medicine. An increasing rate of bacterial resistance to antibiotics has led to treatment failure in some cases of shigellosis in children, and underlines a need for safe, efficient and valid options. OBJECTlVE: The purpose of this study is to evaluate the efficacy of R. ribes syrup as a complementary medicine for treatment of shigellosis in children. DESlGN, SETTlNG, PARTlClPANTS AND lNTERVENTlONS: This randomized, double-blind, placebocontrolled trial started with a group of 150 children aged between 12–72 months with suspected Shigella dysentery. R. ribes syrup or placebo syrup was administered to the intervention and control groups, respectively for 5 days. In addition, the standard antibiotic treatment (ceftriaxone for the first 3 days and cefixime syrup for 2 further days) was administered to both groups. MAlN OUTCOME MEASURES: Body temperature, abdominal pain, need for antipyretics, defecation frequency, stool volume and consistency and microscopic stool examination were recorded as outcome measures. Any observed adverse effects were also recorded. RESULTS: Mean duration of fever and diarrhea in the R. ribes group was significantly lower than that in the placebo group (P = 0.016 and 0.001, respectively). In addition, patients in the R. ribes group showed shorter duration of need for antipyretics and shorter duration of abdominal pain (P = 0.012 and 0.001, respectively). However, there were no significant differences between the two groups regarding the microscopic stool analyses. Furthermore, no adverse effect was reported.CONCLUSlON: R. ribes syrup can be recommended as a complementary treatment for children with Shigella dysentery. TRlAL REGlSTRATlON: Iranian Registry of Clinical Trial: IRCT2014070518356N1.