Pfam family DUF1023 consists entirely of uncharacterized proteins generated by sequencing the genomes of Actinobacteria (Bateman A., et al., Nucleic Acids Res. 2004;32 Database issue:D138–141.) Utilizing sequence similarity detection methods, we infer homology between DUF1023 and α/β hydrolases. DUF1023 proteins conserve the core secondary structures in α/β hydrolase fold, and share similar catalytic machinery as that of α/β hydrolases. We predict DUF1023 spatial structure and deduce that they function as hydrolases utilizing catalytic Ser-His-Asp triad with the serine as a nucleophile. Proteins 2005. © 2005 Wiley-Liss, Inc.