A corrinoid protein was induced and overexpressed in methanol-grown cells of the thermophilic anaerobic bacterium Moorella thermoacetica. The protein was purified from cytosolic extracts. After screening for crystallization conditions and optimization, crystals were obtained that diffracted strongly on a rotating-anode X-ray source. A diffraction data set was collected and processed including reflections to 1.9 Å resolution. Reflections were indexed in a primitive orthorhombic cell with unit-cell parameters a = 55.69, b = 62.74, c = 34.54 Å. N-­terminal amino-acid sequencing indicates that the crystals contain a C-­terminal fragment of the protein.