Crystals of an extracellular beta-galactosidase from Penicillium sp. (MW = 120 +/- 5 kDa) have been obtained from a sodium phosphate buffer using PEG as precipitant. The crystals belong to the tetragonal space group P4(1)or P4(3), with unit-cell parameters a = b = 110.82, c = 161.28 A, and diffract to 1.85 A resolution at a synchrotron source.