Tomographic imaging techniques are attractive tools for the visualization of the internal structural characteristics of pharmaceutical solid dosage forms. In this paper, the internal structure of the tablet core for a monolith osmotic drug delivery system, felodipine sustained-release tablet, was visualized via synchrotron radiation X-ray computed microtomography during the drug release process. The surface areas and three dimensional parameters of the tablet core were calculated based on the three dimensional reconstruction of the images. At different stages of the drug release process, the surface morphology, the hydration, the swelling, and the structure changing of the tablet, were visualized from the two dimensional monochrome X-ray images. The three dimensional volumes of the remaining tablet core correlated well with the percentages of felodipine (R=0.9988). Also, the three dimensional surface area almost unchanged during the drug release process, which clearly demonstrated the intrinsic drug release mechanism of the osmotic drug delivery system. In conclusion, the synchrotron radiation X-ray computed microtomography, with rapid acquisition, high intensity and micro-scale spatial resolution, was found to be a useful tool for the quantitative elucidation of the intrinsic drug release kinetics and the three dimensional parameters such as surface areas of the remained core obtained by the synchrotron radiation. Thus, X-ray computed microtomography can be considered as a new and complimentary analytical tool to standard compendial pharmaceutical tests for quality control of osmotic drug delivery systems.