Background: Iron deficiency anemia (IDA) is one of the most common nutritional disorders worldwide, affecting approximately 30% of the global population. Reticulocyte hemoglobin (Ret-He) reflects the amount of hemoglobin in reticulocytes and provides a real-time indicator of iron availability during erythropoiesis. Unlike conventional iron parameters, Ret-He is less affected by inflammation and infection, making it a more sensitive and reliable marker of functional iron status. It enables early detection of iron deficiency from the initial stage of depleted iron stores and is therefore valuable for early diagnosis and treatment monitoring of IDA. However, studies on the clinical application of Ret-He for early diagnosis and follow-up of IDA remain limited in Mongolia, prompting the present study. Aim: To determine reticulocyte hemoglobin (Ret-He) levels in patients with iron deficiency anemia and to compare them across the severity of anemia. Materials and Methods: A total of 100 patients with hypochromic microcytic anemia who presented to the First Central Hospital were included in the study. The relationship between erythrocyte indices, including hemoglobin (HGB) and reticulocyte hemoglobin (Ret-He), was analyzed according to the severity of anemia. Data were analyzed using Stata version 14. Results: The study included 100 participants aged 18–81 years, of whom 8%(n=8) were male and 92%(n=92) were female. The mean age was 52.8±22.6 years in males and 43.7±16.08 years in females. The leading causes of anemia were uterine bleeding (68%), gastrointestinal disorders (18%), malignancies (10%), and other causes (4%). The mean Ret-He level was 16.15±2.66 pg in males and 19.35±2.08 pg in females, indicating a statistically significant sex difference (p<0.05). Red blood cell count, hemoglobin, MCV, MCH, and Ret-He all decreased progressively with increasing severity of anemia, with statistically significant differences between groups (p<0.0001). Hemoglobin levels showed a significant positive correlation with Ret-He (p<0.001). Conclusion In iron deficiency anemia, reticulocyte hemoglobin levels are significantly reduced and correlate strongly and positively with hemoglobin. The progressive decline in Ret-He with increasing severity of anemia reflects impaired iron availability in the bone marrow. Therefore, Ret-He is a clinically valuable biomarker for early detection of iron deficiency, monitoring treatment response, and assessing anemia severity.