Acetolactate synthase (ALS) catalyzes the chemical reaction in plants and microorganisms that converts two pyruvate molecules to an acetolactate molecule and a carbon dioxide. To confer change on its substrate specificity for one carbon chemicals, structural study was initiated. For this, the recombinant ALS protein from Hydrogenobacter thermophilus(HtALS) was expressed in Escherichia coli, and homogeneously purified. The purified HtALS protein was crystallized from the precipitant composed of 0.3 M Ammonium sulfate, 0.1 M Sodium cacodylate (pH 6.5), and 18% (w/v) polyethylene glycol 4000. Diffraction data was collected to 2.4 ? resolution. The crystal belongs to the primitive orthorhombic P212121 space group with unit-cell parameters a = 75.24 ?, b = 76.62 ?, c = 194.69 ?, and α = β = γ = 90°. There are two HtALS molecules in the asymmetric unit.