Background. Reduced iron is one of the most commonly used iron fortificants, because of its low cost and lack of chemical reactivity. The bioavailability of this fortificant has not been reliably measured in humans because of technical difficulties. Objective. To assess iron bioavailability of wheat flour fortified with reduced iron. Methods. Homemade bread fortified with two reduced iron compounds was produced. We used an in vitro digestion and the Caco-2 cells model to measure the bioavailability of two types of reduced Fe (8 and >20 μm particle size), using ferritin formation by Caco-2 cells and intracellular Fe concentration as indicators of Fe incorporated to the enterocyte. Results. In vitro digestion experiments showed higher values of solubility and dialyzability of reduced-8 μm Fe compared to reduced >20 μm Fe. Intracellular iron and ferritin concentrations in Caco-2 cells exposed to digest from bread fortified with reduced-8 μm Fe were higher than in bread fortified with reduced >20 μm Fe. When bread fortified with FeSO4:ascorbic acid (molar ratio 1:2) was used as a reference, the relative iron bioavailabilities of the bread fortified with reduced-8 μm Fe or >20 μm Fe were 68.2% and 31.1 %, respectively. Conclusion. Reduced iron is a good compound to be used in wheat flour fortification