Ribosomal protein L2 from Bacillus stearothermophilus, a single polypeptide chain with 275 amino acid residues, is a primary 23S rRNA-binding protein in the large ribosomal subunit. Crystals of a 23S rRNA binding domain (BstL2-RBD: positions 60-201) of the ribosomal protein L2 from B. stearothermophilus overexpressed in Escherichia coli have been grown in 0.1 M MES (pH 6.5) containing 15% polyethylene glycol 20 000. The crystals diffract to 2.3-Angstrom resolution on a synchrotron X-ray source. The crystal belongs to the space group P1 and the unit cell axes are a = 28.05, b = 36.20, c = 69.14 Angstrom, alpha = 99.58 degrees, beta = 95.86 degrees, and gamma = 102.62 degrees. There are two molecules of the BstL2-RBD in the asymmetric unit.