A novel ultrafast-laser-based x-ray source is a promising candidate for replacement of a microfocal X-ray tube in a micro-CT system for small-animal imaging. We optimized conditions for x-ray generation from a very small (below 5 μm) focal spot. We measured x-ray spectra, conversion efficiency, x-ray fluence, and x-ray focal-spot size for a number of solid targets (SiO 2, Ge, Mo, Ag, Sn, BaF2, La, Nd, Gd, Ta, and Pb). X-ray spectra created by ultrafast laser are advantageous for micro-CT imaging, because most of the emission is in narrow characteristic lines. The spectra can be changed rapidly and matched to the imaging task. They make practical the use of dual-energy micro-CT with suitable contrast agents and matching targets and filters for low- and high-energy beams. We have obtained images of small animals in single- and dual-energy modes.