Objective: To determine the adverse effects of formula milk in infants presented to our institution. Study Design: Retrospective/observational Place and Duration:The study was conducted at Paediatric Department of Liaquat University Medical Hospital Jamshoro and Civil Hospital Khairpur Mir's. Methodology: Total 85 formula-fed infants of both genders with ages upto 2 years were included in this study. Detailed demographics including age, sex, weight, residence and socio-economic status were recorded after taking informed written consent from guardians/parents. Adverse effects such as iron deficiency, low weight, gastroenteritis, type I diabetes mellitus and autoimmune disease were examined. Data was analyzed by SPSS 24.0. Results: There were 45 (52.94%) females whiles 40 (47.06%) were males. Mean age was 1.86±1.02 years. 52 (61.18%) patients had urban residence and majority 50 (58.82%) had high socio-economic status. Iron deficiency was found in 38 (44.71%) infants, 32 (37.65%) infants had abnormal low weight, 24 (28.24%) had gastroenteritis/diarrhea, 18 (21.18%) infants had type I diabetes and 14 (16.47%) infants had autoimmune disease. Conclusion: It is concluded that formula milk was associated with many of adverse effects, the most common was iron deficiency and low weight. Mothers should be aware of these adverse effects of formula fed. Keywords: Formula Milk, Infants, Iron Deficiency, Low Weight, Infection, Type I Diabetes