Abstract: Objective  To clone and express the malate dehydrogenase（MDH） gene of Toxoplasma gondii，　and analyze the immunogenicity.  Methods  Total RNA was extracted from tachyzoites of RH strain of T. gondii（GenBank accession No. AY650028）. The coding region of TgMDH was amplified with a pair of specific primers. The product of RT?鄄PCR was digested with double restriction enzyme and ligated into pET30a（+） vector. The recombinant pET30a（+）-TgMDH plasmid was transformed into E. coli DH5α. The positive clones were confirmed by the double restriction enzyme digestion， PCR and sequencing. The correct plasmid was transformed into E. coli BL21 and induced by IPTG. The expressed proteins were analyzed by SDS-PAGE. Conditions for expression were optimized. Abundant soluble rTgMDH protein was purified with Ni-NTA affinity chromatography. Mice was intranasally immunized with purified rTgMDH and murine anti-rTgMDH serum was prepared. Western blotting with murine anti-rTgMDH serum and rabbit anti-T. gondii serum was used to analyze its immunogenicity.　 Results 　The product of RT-PCR was with 951 bp. The recombinant plasmid pET30a（+）?-TgMDH was confirmed by the double restriction enzyme digestion，　PCR and sequencing. A soluble recombinant protein with relative molecular weight of 36 000 was analyzed by SDS-PAGE，　followed by coomassie blue staining. Western blotting revealed that rTgMDH can be recognized by murine anti-rTgMDH serum and rabbit anti-T.  gondii serum. 　Conclusion　 TgMDH gene has been expressed in prokaryotic expression system and shows immunogenicity.

Key words: Toxoplasma gondii, Malate dehydrogenase, Prokaryotic expression, Immunogenicity