A cDNA of 1694 bp was cloned from human liver Marathon cDNA by means of Rapid Amplification of cDNA Ends (RACE). The cDNA has an open reading frame at 43-1530 bp encoding 495 amino acid residues and a 17-residue signal peptide. There are four Igc2 domains in the translated polypeptide, which is highly homologous to the human alpha-1B glycoprotein isolated from human plasma. Upon this, we conclude that this cDNA is the alpha-1B glycoprotein precursor gene which has never been cloned before, and it may be a novel member of immunoglobulin superfamily and may involved in the cell recognition and the regulation of cell behavior.