An apparatus and method for acquiring an optimal MEX image may include an X-ray source to generate an X-ray and to irradiate the X-ray, an energy identification detector to acquire a MEX image that is generated when the irradiated X-ray penetrates an object, and an optimal MEX processor to generate an optimal MEX parameter based on a characteristic of the object and to control at least one of the X-ray source and the energy identification detector based on the generated optimal MEX parameter.