Breast density is more and more considered as an important risk factor for breast cancer and several quantitative breast density evaluation methods have been proposed. The reference material for simulation of the breast attenuation proper-ties of glandular and adipose breast tissues is manufactured by a single provider. In order to characterize the attenuation properties of these materials, measurements in Hounsfield Units (HU) have been performed using a CT-scanner. Breast-equivalent plates have been imaged in different configurations (plates in and orthogonal to image planes), providing consistent results (+ 1.3 HU). Breast density equivalent plates of different nominal breast density equivalences and sizes were measured, demonstrating both a good homogeneity within the plates (+ 1.8 HU) and a good consistency between plates of the same nominal breast density equivalence (+ 1.5 HU). In addition, dual energy CT provided mono-energetic HU from which mono-energetic linear attenuation coefficients of water and glandular and adipose equivalent materials were computed. The values for these coefficients were found in good agreement with results from literature, respectively direct mono-energetic measurements of breast samples, and computation by combining published breast tissue atomic compositions and linear attenuation coefficient tables. In conclusion, CT was found effective for the verification of the breast equivalent material, and the homogeneity and consistency of the plates were found satisfactory. Furthermore, the most recent spectral CT technology allowed demonstrating a good agreement of the attenuation properties of breast-equivalent material plates with state-of-the-art knowledge of real breast tissue attenuation.