A three-dimensional medium-energy ion scattering spectrometer has been developed for crystallographic structure analysis of nanomaterials. Three-dimensional medium-energy ion scattering spectroscopy (3D-MEIS) is an outgrowth of medium-energy coaxial impact-collision ion scattering spectroscopy (ME-CAICISS). A pulsed He + ion beam at 100 keV is incident upon a sample, and scattered (and/or recoiled) particles are detected by a position-sensitive and time-resolving microchannel plate (MCP) detector with two delay-line anodes, which provides information on the two-dimensional blocking pattern and flight time of scattered (and/or recoiled) particles. Preliminary experiments using 3D-MEIS have been made for a Si(1 1 1) crystal. The blocking pattern of a Si crystal was clearly observed, which indicated that the performance of the spectrometer was satisfactory.