Bone morphogenetic protein (BMP) belongs to the cytokine and transforming growth factor beta (TGF-β) superfamily and plays an important role in embryo morphogenesis and organ formation. However, it currently lacks various antibodies to the BMP signaling pathway factor SAX. In this paper, the total RNA was extracted from Drosophila embryos, and the cDNA library was obtained by reverse transcription. The SAX gene fragment was obtained by PCR using the cDNA as a template, and the fragment was ligated into pCAGGS-P7 to construct a recombinant plasmid pCAGGS-P7-sax. BALB/C mice were immunized with plasmid DNA immunoassay to prepare polyclonal antibodies against Drosophila SAX protein. Further analysis showed that the constructed eukaryotic expression recombinant plasmid pCAGGS-P7-sax DNA had good immunogenicity, and the anti-serum antibody titer obtained after immunization of mice reached 1∶100. Western blot and Drosophila embryo immunofluorescence assay showed that antiserum can specifically recognize SAX protein. The successful preparation of Drosophila SAX antibody laid the foundation for further study of the role of sax gene and BMP signal in Drosophila heart development.