Background. Xyloglucan, a film-forming agent, improves intestinal mucosa resistance to pathologic damage. The efficacy, safety, and time of onset of the antidiarrheal effect of xyloglucan were assessed in children with acute gastroenteritis receiving oral rehydration solution (ORS). Methods. This randomized, controlled, open-label, parallel-group, multicenter, clinical trial included children (3 months-12 years) with acute gastroenteritis of infectious origin. Children were randomized to xyloglucan and ORS, or ORS only, for 5 days. Diarrheal symptoms, including stool number/characteristics, and safety were assessed at baseline and after 2 and 5 days and by fulfillment of a parent diary card. Results. Thirty-six patients (58.33% girls) were included (n = 18/group). Patients receiving xyloglucan and ORS had better symptom evolution than ORS-only recipients, with a faster onset of action. At 6 hours, xyloglucan produced a significantly greater decrease in the number of type 7 stools (0.11 versus 0.44; P = 0.027). At days 3 and 5, xyloglucan also produced a significantly greater reduction in types 6 and 7 stools compared with ORS alone. Xyloglucan plus ORS was safe and well tolerated. Conclusions. Xyloglucan is an efficacious and safe option for the treatment of acute gastroenteritis in children, with a rapid onset of action in reducing diarrheal symptoms. This study is registered with ISRCTN number 65893282.