A highly thermostable xylose isomerase from Thermus thermophilus has been expressed in Escherichia coli and crystallized. The purified enzyme shows its optimum temperature at $90^{circ}C$. It has been crystallized at room temperature using polyethylene glycol 4000 as the precipitant. The crystal belongs to the orthorhombic space group $P2_12_12_1$, with unit cell parameters of a = 73.34 ${AA}$, b = 144.05 ${AA}$, c = 155.07 ${AA}$. The presence of one molecule of tetrameric xylose isomerase in the asymmetric unit gives a crystal volume per protein mass ($V_m$) of 2.32 ${AA}^3/Da$ and the solvent content of 47.0% by volume. The diffraction pattern extends to 1.9 ${AA}$ Bragg spacing with synchrotron radiation and a set of native data has been collected to 2.3 ${AA}$.