Ferredoxin reducatase component of a biphenyl dioxygenase derived from Pseudomonas sp. strain KK.S102 has been crystallized using sodium formate as the precipitant. The crystal belongs to the space group P6122 (or P6522) with cell parameters of a= b = 99.5 A, c = 175.6 A, and diffracts to 2.5 A resolution.