Iron nanoparticles (Fe-NPs) have recently been used for cancer diagnosis and therapy for imaging contrast and drug delivery. However, no study on nutritional bioavailability of Fe-NPs in the body has been reported. Ascorbic acid (AA) is known to aid in absorption of iron in the stomach by reducing Fe (III) to Fe (II). In this study, we investigated the bioavailability of Fe-NPs with AA in iron-deficiency-anemic mice in comparison with non-nano iron particles. Iron-deficient anemia was induced by feeding an iron-deficient diet (4.5 mg Fe/kg) and ocular bleeding from retro-orbital venous plexus for four weeks. Normal control mice were given a normal diet (45 mg Fe/ kg). After induction of anemia in mice, anemic mice received daily oral administration of Fe (40 mg/kg B.W.) + AA (5 g/kg B.W) and Fe-NPs (40 mg/kg B.W) + AA (5 g/kg B.W). After sacrifice, liver and spleen tissues were observed by haematoxylin & eosin stain. Amount of trace iron in liver and upper small intestine was investigated using an inductively coupled plasma-atomic emission spectrometer. Red blood cells (RBC), hematocrit (Hct), hemoglobin (Hb), and total iron binding capacity were also measured. The concentrations of iron in the Fe-NPs + AA group were significantly higher in liver and in upper small intestine than that in the Fe + AA group. The values of RBC, Hct, and Hb in the Fe-NPs + AA group were more rapidly increased to normal values compared with the Fe + AA group with increasing time. These results suggest that Fe-NPs in the presence of AA may be more bioavailable than non-nano Fe in Fe-deficient anemic mice.