The high-affinity receptor for immunoglobulin E (IgE), FcepsilonRI, is specifically expressed in mast cells and basophils and plays a key role in IgE-mediated allergic reactions. The transcription factor Elf-1 has been previously identified to bind to the promoter of the human FcepsilonRI alpha-chain, which is essential for the function and expression of FcepsilonRI. In the present study, Elf-1 siRNA was conducted to evaluate the effects of Elf-1 on FcepsilonRI alpha-chain expression in the primary mouse mast cells, bone marrow-derived mast cells (BMMC). Introduction of Elf-1 siRNA effectively reduced expression levels of Elf-1 mRNA and protein in BMMC. Transient reporter assay showed that the knockdown of Elf-1 by siRNA resulted in increased FcepsilonRI alpha-chain promoter activity, while overexpression of Elf-1 suppressed alpha-chain promoter activity in BMMC. Elf-1 siRNA-treated BMMC exhibited marked upregulation of FcepsilonRI alpha-chain transcription, whereas beta-chain mRNA was not affected by Elf-1 siRNA. Chromatin immunoprecipitation assay showed that the amount of transcription factor PU.1, recognizing the cis-element close to the Elf-1-site on the FcepsilonRI alpha-chain promoter, was significantly increased by introduction of Elf-1 siRNA. These results indicate that Elf-1 negatively regulates FcepsilonRI alpha-chain expression by suppressing PU.1-mediated transcription of the alpha-chain in BMMC.