The present invention provides a polypeptide protein dimer comprising two monomers comprising an extracellular domain of an alpha subunit of an IgE Fc receptor (FcεRIa-ECD). The protein dimer according to the present invention is excellent in IgE binding ability and lacks ADCC and CDC functions when compared with a conventional therapeutic agent comprising an anti-IgE antibody, and has an advantage of fewer other side effects, and therefore, the protein dimer may be applied to medicine for therapeutic or prophylactic use against allergic diseases mediated by IgE.
