A digital x-ray imaging system for small animal studies is introduced. The detector of the system consists of a scintillating screen fiber-optically coupled to two 1024×1024 CCD image arrays. The optical coupling provides about 2 demagnification to math the pixel size at the scintillating screen to the CCD element size. Therefore, the effective pixel size of the detector is 48 μm with the CCD imaging array gives 24 μm pixel spacing. The focal-spot size of the x-ray tube is 20 μm. The x-ray source uses a tungsten target with a 0.25mm-thick beryllium window. The tube current of this system is 0.3mA fixed, and the tube potential from 10 to 35kVp adjustable. The exposure time can be adjusted from 0.1 to 999s. The system can offer the magnification of 1×, 1.5×, 2×, 3×, 4×, and 5×, respectively. The physical characteristics in terms of spatial resolution, noise, and SNR of a CCD based digital x-ray imaging system for small animal studies have been investigated. They are evaluated by measuring modulation transfer function (MTF), noise power spectrum (NPS) and noise equivalent quantum (NEQ). The MTF,NPS and NEQ of three different areas of the CCD detector show high consistency of the three different areas of the CCD detector. The MTF of digital x-ray imaging system different magnifications show the trend of resolution increase as the magnification increasing. NPS and NEQ at different exposure dose are presented as well, which show the trend of noise and the number of Poisson-distributed quanta giving the same signal-to-noise ratio as the exposure dose increasing. Moreover, preliminary tests have been carried out on several samples in order to evaluate the performance of the digital x-ray imaging system. A conclusion can be made that the digital x-ray imaging system can be used to carry out high-resolution analysis in vitro, or in vivo of biomedical samples by proper application.