The high-affinity IgE receptor (FcepsilonRI)-beta gene is one of the atopy-associated genes, but its biological significance is largely unknown. In this study, we generated the anti-FcepsilonRI-beta chain antibody to clarify beta-chain protein expression in human mast cells. The FcepsilonRI-beta antibody showed specific binding to a 27 kDa protein with Western blotting and membrane bound immunostaining using cultured mast cells. Monomeric IgE sensitization increased beta-chain expression as well as mature alpha-chain expression in mast cells. Upregulation of beta-chain expression with monomeric IgE treatment suggests possible roles of FcepsilonRI-beta protein as an atopy-related molecule.