The aim of the present study was to evaluate ZnS:Cu phosphor for use in X-ray mammographic detectors. This phosphor has never been used in medical imaging probably due to its moderate scintillation decay time. However, it may be suitable for non-dynamic medical imaging, due to its “green” emission spectrum, which is compatible with the sensitivity of many currently used photodetectors, and its high X-ray to light intrinsic conversion efficiency. ZnS:Cu phosphor powder was used to prepare several test screens in laboratory. Parameters related to light emission and image quality properties were experimentally as well as theoretically evaluated and compared to those of other known ZnS-based phosphor materials. Results showed that ZnS:Cu performed adequately well in the mammographic energy range.