Platelet glycoprotein (GP) Ib/IX/V complex is a major receptor for von Willebrand factor (vWF), which mediates platelet adhesion and aggregation under high shear stress conditions. It is composed of GPIb alpha, GPIb beta, GPIX, and GPV. All subunits for the human receptor have been cloned and characterized. However, the function of GPIb beta is still elusive. To obtain further information of GPIb beta, we have determined the genomic sequence of mouse GPIb beta (1466 bp). The deduced amino acid sequence (206aa) was 88% identical to the human GPIb beta protein. All cysteine residues, putative N-linked glycosylation site (Asn41), and putative phosphorylation site (Ser166) were conserved. The promoter region contained putative GATA and ets binding motif implicated in megakaryocytic expression. Mouse GPIb beta also contained a leucine-rich glycoprotein (LRG) sequence of 24 amino acids same as human GPIb beta.