Background. The association between obesity and different types of anemia remained uncertain. The present study aimed to assess the relation between obesity parameters and the occurrence of iron deficiency anemia and also megaloblastic anemia among Iranian population.Methods and Materials. This cross-sectional study was performed on 1252 patients with morbid obesity that randomly selected from all patients referred to Clinic of obesity at Rasoul-eAkram Hospital in 2014. The morbid obesity was defined according to the guideline as body mass index (BMI) equal to or higher than 40 kg/m 2 . Various laboratory parameters including serum levels of hemoglobin, iron, ferritin, folic acid, and vitamin B12 were assessed using the standard laboratory techniques.Results. BMI was adversely associated with serum vitamin B12, but not associated with other hematologic parameters. The overall prevalence of iron deficiency anemia was 9.8%. The prevalence of iron deficiency anemia was independent to patients' age and also to body mass index. The prevalence of vitamin B12 deficiency was totally 20.9%. According to the multivariable logistic regression model, no association was revealed between BMI and the occurrence of iron deficiency anemia adjusting gender and age. A similar regression model showed that higher BMI could predict occurrence of vitamin B12 deficiency in morbid obese patients.Conclusion. Although iron deficiency is a common finding among obese patients, vitamin B12 deficiency is more frequent so about one-fifth of these patients suffer vitamin B12 deficiency. In fact, the exacerbation of obesity can result in exacerbation of vitamin B12 deficiency.