The aim of the present study was to examine the light emission efficiency of Lu2SiO5:Ce (LSO) powder scintillator under X-ray mammographic imaging conditions. LSO is an efficient and extremely fast scintillator, employed in positron tomography, which however has never been used in X-ray imaging. For the purposes of the present study a 25 mg/cm2 thick scintillating screen was prepared in our laboratory, by sedimentation of Lu2SiO5:Ce powder. Absolute luminescence efficiency measurements were performed within the range of X-ray tube voltages (22-40 kVp) used in mammographic applications. Parameters related to X-ray detection, i.e. the energy absorption efficiency and the quantum detective efficiency were calculated. A theoretical model, describing radiation and light transfer, was employed to fit experimental data and to estimate values of the intrinsic conversion efficiency and the light attenuation coefficients of the screen. The Lu2SiO5:Ce powder scintillator material showed to exhibit high radiation absorption properties in comparison with Gd2O2S:Tb and CsI:Tl and considering its very short decay time, it may successfully be employed in digital mammography.