The TON_0887 gene product from Thermococcus onnurineus NA1 is a 240-residue protein that has histidinol-phosphate phosphatase (HolPase) activity. According to analysis of its primary structure, the TON_0887 gene product is a monofunctional HolPase that belongs to the DDDD superfamily. This contrasts with the generally accepted classification that bifunctional HolPases belong to the DDDD superfamily. The TON_0887 gene product was purified and crystallized at 295 K. A 2.2 A resolution data set was collected using synchrotron radiation. The TON-HolPase crystals belonged to space group P222(1), with unit-cell parameters a = 40.88, b = 46.89, c = 148.03 A. Assuming the presence of one molecule in the asymmetric unit, the solvent content was estimated to be about 48.3%.