Breast density is a well-recognized important breast cancer risk factor. However, accurately assessing breast density is difficult. Although the mammographic density is the most popular method to assess breast density in current clinical practice, it is not accurate and reliable due to the overlap of breast tissues and inter-reader variability. In order to more accurately assess breast density, we proposed a new non-invasive assessment technology based on the measurement of dielectric impedance spectrums of the breast regions. The objective of this study is to test the feasibility of this new technology through a unique phantom study. The phantom design is based on mixing two types of agar saline materials with two different levels of electrical conductivity corresponding to fat and fibro-glandular tissue conductivities. In the phantom design considerations, we assembled four breast phantoms to mimic four breast density categories defined by the Breast Imaging Reporting and Data System. The testing results showed that as the increase of the simulated "fibro-glandular" tissues inside the phantom, the measured electrical impedance values monotonically decreased. The testing results were consistent and reproducible at different positions between detection probes and breast phantom surface when considering and calibrating the systematic errors. Thus, this study demonstrated the feasibility of developing and applying a new dielectric impedance measurement technology and device to assess breast density, which is low-cost, non-invasive, non-hazard and easy-to-use. If successful in future tests, this new method has potential to assist better assessing breast cancer risk for developing an optimal personalized breast cancer screening paradigm.