Background/aim: Iron deficiency anemia (IDA) affects hemoglobin A1c (HbA1c) levels. This study aimed to evaluate the effect of treatment of iron deficiency anemia on hemoglobin A1c in type 2 diabetic patients.Materials and methods: Ninety type 2 diabetes mellitus (T2DM) patients with IDA were included in a randomized, placebo-controlled, single-blind clinical trial. The intervention group (n = 45) received 200 mg/day oral iron for 3 months and the control group (n = 45) received an oral placebo for the same period. Fasting blood sugar, complete blood count, and HbA1c were measured for all subjects at the beginning and the end of the trial.Results: The mean age of the treatment and control group was 51.47 $\pm$ 1.05 and 52 $\pm$ 1.1 years, respectively. The two groups were not statistically significantly different with regard to diabetes duration (P = 0.436) and age (P = 0.617). Hemoglobin, mean corpuscular volume, mean corpuscular hemoglobin, serum iron, ferritin, total iron-binding capacity, and HbA1c were significantly improved in the intervention group in comparison with the control group (P = 0.005).Conclusion: Iron status should be considered during the interpretation of the HbA1c concentrations in diabetes mellitus. Iron replacement therapy can decrease HbA1c in anemic patients with IDA and T2DM.