While breast density is known as one of the critical risk factors of breast cancer, Digital breast tomosynthesis (DBT)-based diagnostic performance is known to have a strong dependence on breast density. As a potential solution to increase the diagnostic performance of DBT, we are investigating dual-energy DBT imaging techniques. We estimated partial path lengths of an x-ray through water, lipid, and protein from the measured dual-energy projection data and the object thickness information. We reconstructed material-selective DBT images for the material-decomposed projection. The feasibility of the proposed dual-energy DBT scheme has been demonstrated by using physical phantoms.