We compared the efficacy of ferrous sulfate (divalent) and ferric polymaltose (trivalent) compounds for the prophylaxis of iron-deficiency anemia (IDA). Study infants included exclusively breast milk-fed term infants. Subjects were divided randomly into 2 groups at 4 months of age and group 1 (n=56) received divalent and group 2 (n=56) received trivalent iron (Fe) preparation at a dose of 2 mg/kg/d for 5 months. At 9 months of age, after a 5-month prophylaxis, a significant increase was observed in hemoglobin (Hb), hematocrit, serum Fe levels, and transferrin saturation in both groups. However, group 1 had significantly higher Hb, hematocrit, mean corpuscular volume, Fe, and transferrin saturation than group 2 (11.7±0.6 g/dL, 34.6%±1.7%, 76.2±2.9 fL, 55.5±1.8 mcg, 20.8±3.9 g/L, respectively in group 1 vs. 11.3±0.5 g/dL, 33.5%±1.5%, 74.7±3.2 fL, 42.5±1.8 mcg, 14.1±7.5 g/L, respectively in group 2). No significant difference was found in ferritin values between the groups. Fe deficiency was found in 17 (30.3%) of the subjects in group 1, and 23 (41%) of subjects in group 2 whereas 5 (8.9%) subjects had IDA in group 1 and 12 (12%) in group 2 which were insignificant between groups. No significant difference was found with regard to side effects between 2 Fe preparations. Although divalent Fe therapy led to a higher Hb and serum Fe level, both ferrous and ferric Fe preparations were effective for prophylactic use in the prevention of Fe deficiency and IDA with comparable side effects.