Glucokinase/hexokinase catalyzes the phosphorylation of glucose to glucose 6-phosphate, which is the first step of glycolysis. The open reading frame TTHA0299 of the extreme thermophile Thermus thermophilus encodes a putative glucokinase/hexokinase which contains the consensus sequence for proteins from the repressors, open reading frames and sugar kinases family. In this study, the glucokinase/hexokinase from T. thermophilus was purified and crystallized using polyethylene glycol 8000 as a precipitant. Diffraction data were collected and processed to 2.02 angstrom resolution. The crystal belonged to space group P21, with unit-cell parameters a = 70.93, b = 138.14, c = 75.16 angstrom, beta = 95.41 degrees.