Background and purpose: Dual-energy mammography is a technique which is used to enhance the accuracy of breast cancer diagnosis especially in dense breasts. This study was conducted based on the simultaneous use of two contrast agents for automatic separation and also to evaluate their accuracy using dual-energy digital mammography. Materials and methods: A breast phantom was designed and built. Different thicknesses of aluminum sheets were imaged for micro-calcification simulation and Iodine and Bismuth contrast agents were placed at various density thicknesses inside the phantom. Also, an X-ray tube with Tungsten anode and a flat panel semiconductor detector Si/GadOx was used for imaging processes. To apply dual-energy imaging, appropriate filter for high-energy spectrum was designed by MCNP-4C Monte Carlo code and built. Matlab software was used for equations solving and image processing. Results: The separation of Iodine images was prepared for thicknesses greater than 0.5 mg/cm2and Bismuth images greater than 0.53 mg/cm2. Conclusion: According to the results, simultaneous isolation of two contrast agent images, I and Bi, from breast tissue were accurately prepared by dual-energy digital mammography via choosing appropriate contrast agent materials and image processing technique. So, this method could help the physicians in making an easy and more accurate diagnosis.