Purpose of study- This study was conducted to evaluate B12 levels in children with macrocytic anaemia and to know the etiology of macrocytosis in children, Materials and the methods-This study was a cross-sectional study carried out over a period of 18 months on 50 children up to 18 years of age of macrocytic anaemia. Children were identified as macrocytic having MCV > 95fl (mean corpuscular volume). Result- In this study for mean haemoglobin of 11 g/dl the RBC volume was at a mean of 95.7. As the haemoglobin level fell the mean MCV increased to 99.93 which was statistically significant Conclusion-Nutritional deficiency is the most common cause of macrocytic anaemia. Vitamin B12 deficiency is a major cause as nutritional anaemia among adolescent females.