Aim: The objective of this study was to determine the effect of diosmectite in reducing the duration of diarrhea in comparison with placebo. Method and material: This open, randomized clinical trial was conducted in the Pediatric Unit of Benazir Bhutto Hospital, Rawalpindi for one-year duration from 1st October 2019 to 30th September 2020. The patients were allotted group A (Diosmectite group) or group B (placebo group) by the lottery method. After the initial hydration Diosmectite at a dose of one gram in children below 12 months of age and 1.5 grams in children 12-24 months of age three times a day diluted in water or other semi-solid food along with zinc sulphate was administered orally for 5 days to group A while group B was given placebo (oral zinc sulphate). All the study participants were followed from the beginning of therapy to normalization defined as the passage of first stool of pre-diarrheal consistency (hours) and maximally for six days from the beginning of therapy in case of failure to pass stool of pre-diarrheal consistency. Results: There were 103 children in each group who were initially recruited into the study. 99 (96.12%) children in the diosmectite group and 97 (94.17%) children in the placebo group completed the study. Both groups had similar characteristics. There were 6 of 99 cases in the diosmectite group, while 7 of 97 in the placebo group that did not produce pre-diarrheal stools at the end of six days after starting treatment (p value 0.782). The time required to pass the first pre-diarrheal stool (hours) for the remaining 93 diosmectites was 58.935 ± 30.482, while the time to pass the first pre-diarrhea stool (hours) for the remaining 90 placebo patients was 76.511 ± 35.323 (value p 0.0004). This showed that the drug was moderately effective compared to placebo. Conclusion: Smectite may be a useful addition to rehydration therapy in the treatment of acute watery diarrhea in children, but cost-effective tests are required before routine use is recommended. Key words: randomized clinical trial of acute diarrhea, drug efficacy.