Objectives: The objective of this particular research was to contrast mean duration of acute diarrhea in infants taking lactose free formula versus lactose-containing formula milk along with standard treatment. Study Design: Randomized Controlled Trial. Setting: Department of Paediatric Medicine DHQ Teaching Hospital Sargodha. Period: 6 months from 29 October 2016 to 28 April 2017. Material & Methods: This study included 60 infants of both genders who were between 1month to 1 year of age and presented with acute diarrhea. These infants were separated into two groups. Infants in Group-A were given lactose-free formula milk while those in Group-B received lactose-containing formula milk. Outcome variable was mean duration of diarrhea which was compared between the two groups. Consent was taken in black and white from parents of each infant. Results: The average age of the infants was 7.2±3.1 months. Majority (n=41, 68.3%) of the infants were aged 6 months and above followed by 19 (31.7%) infants aged between 1-5 months. There were 29 (48.3%) male and 31 (51.7%) female infants with a female to male ratio of 1.1:1 the weight of infants ranged from 2.6 Kg to 11.9 Kg with a mean of 8.1±2.2 Kg. Both study groups were compared in terms of mean age (p-value=0.741), mean weight (p-value=0.932) and age (p-value=0.781), gender (p-value=0.438) and weight (p-value=0.573) groups distribution. The mean period of diarrhea was notably shorter in infants taking lactose-free milk (1.7±0.8 vs. 2.7±0.8 days; p<0.001) as compared to those receiving lactose-containing milk. Similar significant differences were observed across various subgroups based on patient’s age, gender and weight. Conclusion: Lactose-free formula milk reduces mean duration of diarrhoea significantly when compared to lactose-containing formula milk regardless of patient’s age, gender and weight which advocate its preferred use in future practice in infants presenting with acute diarrhea.