An apparatus and method for estimating object information is provided. The object information estimating apparatus includes a database which stores phantom information obtained by projecting a first energy X-ray on a phantom, an input unit which receives first object information obtained by projecting the first energy X-ray an an analysis object, and which receives information on a thickness of the analysis object, and an estimating unit which estimates second object information based on the phantom information, the first object information, and the information on the thickness.
