Alginate lyase A1-II of Sphingomonas species A1 was purified and crystallized using the hanging drop vapor-diffusion method in 0.1 M Tris-HCl buffer containing 43% saturated ammonium sulfate, 8% polyethylene glycol 4000 and 0.2 M Li(2)SO(4) at pH 8.5 and 20 degrees C. The crystals are tetragonal and belong to the space group P4(3)2(1)2 or P4(1)2(1)2 with unit cell dimensions of a=b=144.07 and c=296.38 A. The diffraction data up to 2.8 A were collected by a synchrotron radiation source at SPring-8 in Japan.