A simple and rapid procedure has been found for the preparation of higly pure alkaline form fructose-1,6-diphosphatase from turkey liver. The protein is tetrameric and is composed of subunits comprised of a 29,000 molecular weight core fragment and an associated 7,000-dalton S-peptide. Large single crystals of the protein, suitable for x-ray diffraction analysis, are produced in the course of the preparation. These are of space group R3 and have rhombohedral cell dimensions of a = 153 A and delta = 163 degrees (equivalent hexagonal dimensions a = 303 A, c = 75 A). There is one entire tetramer of 144,000 daltons in the asymmetric unit. The enzymatic properties of this enzyme appear to be very similar to those reported for the protein from other organisms, but its unique propensity to crystallize opens the way for a full three-dimensional structural analysis.