Dissimilatory sulfite reductase (dSiR, DsrAB) is a key protein in dissimilatory sulfur metabolism, one of the earliest types of energy metabolism to be traced on earth. dSirs are large oligomeric proteins around 200kDa forming an α 2 β 2 arrangement and including a unique siroheme-[4Fe–4S] coupled cofactor. Here, we report the purification, crystallization and preliminary X-ray diffraction analysis of dSir isolated from Desulfovibrio vulgaris Hildenborough, also known as desulfoviridin. In this enzyme the DsrAB protein is associated with DsrC, a protein of unknown function that is believed to play an important role in the sulfite reduction. Crystals belong to the monoclinic space group P2 1 with unit-cell parameters a=122.7, b=119.4 and c=146.7Å and β =110.0°, and diffract X-rays to 2.8Å on a synchrotron source.