6-Aminohexanoate-oligomer hydrolase (NylC) from Agromyces sp. KY5R was expressed in Escherichia coli JM109 and purified by ammonium sulfate fractionation, anion-exchange column chromatography and gel-filtration chromatography. NylC was crystallized by the sitting-drop vapour-diffusion method with sodium citrate as a precipitant in 0.1 M HEPES buffer pH 7.5 containing 0.2 M NaCl. Diffraction data were collected from native and K(2)PtCl(4)-derivative crystals to resolutions of 2.00 and 2.20 Å, respectively. The obtained crystal was plate-shaped, with an I-centred orthorhombic space group and unit-cell parameters a = 155.86, b = 214.45, c = 478.80 Å. The anomalous difference Patterson map of the K(2)PtCl(4)-derivative crystal suggested that the space group was I222 rather than I2(1)2(1)2(1).