Background: Low lactase levels in Asian children appear to be genetically determined or rotavirus-induced gastroenteritis. Consuming lactose-free formula in children with acute gastroenteritis may shorten diarrhea's duration and increase weight gain. This study aims to determine whether lactose-free milk will change the duration of diarrhea and weight gain in Vietnamese children aged 2-24 months with acute gastroenteritis.Materials and methods: A randomized control trial was performed on 66 children under 24 months of age with acute gastroenteritis at the Gastroenterology Department of Can Tho Children's Hospital. In adjunction to oral rehydration solution, they received either a lactose-free formula (n=33) or a lactose-containing formula (n=33).Outcome measures: Diarrhea duration, weight gain, treatment failure, and days of hospitalization were all studied.Results: A total of 66 children participated in this trial, with a mean age of 13.4 ± 5.1 months, and 38 participants (57.6%) were male. There were no significant differences between the lactose-free formula group and the lactose-containing formula group in the duration of diarrhea (2.2±0.8 days versus 2.4±0.9 days; P=0.321), percentage of weight gain (1.96 [IQR:1.35-2.36] percent vs. 2.29 [IQR:1.81-2.40] percent; P=0.131), treatment failure rate (33.3% vs. 36.4%; P= 0.796), and days of hospitalization (5.8±1.7 vs. 6.5±2.5 days; P=0.158).Conclusions: It may not be necessary to use lactose-free milk routinely in Vietnamese children under 24 months with acute gastroenteritis as the duration of diarrhea, weight change, treatment failure rates, and hospital stay are similar to those of children fed lactose-containing milk.