A new rod-pinch polycapillary-coupled x-ray diffraction (XRD) system is being developed as a transmission mode XRD diagnostic for dynamic materials experiments at Sandia National Laboratories’ Thor pulsed-power generator. The Thor pulsed-power generator produces an electromagnetic drive for high-pressure ramp compression experiments to determine dynamic material properties. Single-pulse XRD, because of its unique ability to observe atomic-scale properties of matter in real time, has become an extremely valuable diagnostic for Thor materials experiments. The newly developed XRD system consists of a 35-stage Marx bank, either a cable-coupled or direct-coupled rod-pinch diode, a point-to-point focusing polycapillary optic, and a cylindrical camera. The XRD system is configured in a focusing Debye-Scherrer transmission mode geometry. A molybdenum rod-pinch anode generates a very small (~0.35 mm diameter) soft x-ray spot, allowing efficient coupling of the 17.4 keV Mo K-alpha x-ray beam into the polycapillary optic. The output of the polycapillary is a monochromatic x-ray beam with a 0.5-degree convergence angle focusing to a 1.0 mm spot 590 mm downstream from the polycapillary optic. This configuration results in improved XRD line resolution compared with the existing pinhole system. Downstream shielding and the large distance from the rod pinch to the XRD camera cause most of the hard x-ray background to be removed from the XRD image, eliminating an inherent problem with the existing pinhole system. Laboratory testing of the new rod-pinch polycapillary-coupled XRD system has shown significant improvements in signal-to-noise ratio and resolution compared with the pinhole XRD system. The results of simulated load target testing and a prototype for the new Thor rod-pinch polycapillary XRD system are described here.