Selenate reductase from Thauera selenatis was crystallized using ammonium sulfate as a precipitant. Crystals of selenate reductase belong to the space group C2, with unit-cell parameters a = 116.9, b = 67.5, c = 186.7 A, beta = 90 degrees. Native data to 2.1 A resolution have been collected and a heavy-atom derivative has been identified following soaking of the crystals in a solution of trimethyl lead acetate.