Background: Imerslund–Gräsbeck syndrome is a rare autosomal recessive disorder caused by mutations affecting the cubam receptor complex (CUBN or AMN genes), leading to selective intestinal malabsorption of vitamin B12. The condition is characterized by early-onset megaloblastic anemia and persistent, non-progressive proteinuria. As vitamin B12 plays a critical role in DNA synthesis and neurological development, delayed diagnosis may result in pancytopenia, growth failure, and irreversible neurodevelopmental impairment. Case presentation: A 1-year-5-month-old girl presented with reduced activity and generalized body swelling. Examination revealed severe pallor, moderate sized hepatomegaly , and generalized edema. There were no dysmorphic features or evidence of chronic liver disease. Initial laboratory investigations revealed profound anemia with hemoglobin of 2.4 g/dL.Peripheral blood and bone marrow smear demonstrated macrocytosis. Serum vitamin B12 levels were markedly reduced, while folate levels were within normal limits. Urinalysis revealed persistent nephrotic-range proteinuria without hematuria. Renal function tests were normal. There was no history suggestive of nutritional deprivation or chronic gastrointestinal disease. Given the combination of severe vitamin B12 deficiency and persistent proteinuria, a diagnosis of Imerslund–Gräsbeck syndrome was considered. The child received packed red cell transfusion followed by intramuscular hydroxocobalamin therapy . Clinical improvement was observed with increased activity and rising hemoglobin levels. Proteinuria was settled gradually . Conclusion: This case highlights the importance of considering Imerslund–Gräsbeck syndrome in infants presenting with severe megaloblastic anemia and unexplained proteinuria. Early recognition and lifelong vitamin B12 replacement are crucial to prevent neurological sequelae and ensure normal growth and development.