BACKGROUND Acute diarrhea is the second most common cause of morbidity and mortality worldwide, especially in children aged ≤3 years. Some drugs (e.g., the mucoprotector gelatin tannate) plus a reduced osmolality oral rehydration solution (ORS) may effectively reduce symptom duration and severity. The current trial was therefore designed to assess the efficacy and safety of gelatin tannate in pediatric patients with acute diarrhea. MATERIAL AND METHODS This was a randomized, controlled, double-blind, parallel-group, single-center study comparing gelatin tannate plus ORS (103 patients) with ORS plus placebo (100 patients) in children aged 3 months to 12 years with infectious or noninfectious acute diarrhea. Details about stool consistency and total time to resolution of diarrhea comprised the primary study endpoints. Secondary study endpoints included symptoms of diarrhea at 12, 24, 36, 48, and 72 hours after the first dose of study medication. RESULTS From 12 hours onwards, the incidence of watery stools was significantly lower in the gelatin tannate group than in the ORS group (at 12 hours: 59.2% vs. 77.0%; p=0.01). The same was true for stool frequency (at 12 hours: mean 2 vs. 3 stool productions in the previous 12 hours; p<0.01). At all timepoints during the study, the proportion of patients with Stool Decrease Index improvement was significantly greater (p<0.01) in the gelatin tannate group than in the placebo group (at 12 hours: 66.6% vs. 33.3%; p<0.01). CONCLUSIONS Gelatin tannate plus ORS is an effective and safe option for the treatment of acute diarrhea in children. Significant symptom relief is evident 12 hours after starting treatment.