Using the wave nature of X-rays, in-vitro phase-contrast X-ray imaging can clearly reveal the detailed inner structures of cancer in human and rabbit. In this study, using a newly developed imaging system with a two-crystal interferometer and the Fourier data acquisition technique, we presented, for the first time, in-vivo phase-contrast X-ray computed tomography (CT) images of cancer implanted in nude mice. The two-crystal interferometer, which helps to eliminate the distortion of the half mirror of an X-ray interferometer due to the heat from live animals, was the key device for successful in-vivo imaging. CT images obtained using the Fourier technique were available in approximately 40 min while the animal was still under anesthesia.