Abstract: Objective  To clone and express rhoptry protein 18（ROP18） gene of Toxoplasma gondii, and analyze its immunoreactivity.  Methods  The genomic DNA was extracted from T. gondii（RH strain） tachyzoites. TgROP18 gene was amplified by PCR, and cloned into pET30a（+） vector. The constructed pET30a（+）-TgROP18 was transformed into E. coli BL21（DE3） and followed by expression of the protein induced by IPTG. The recombinant protein was analyzed through SDS-PAGE, and identified by Western blotting with mouse anti-T. gondii serum.  Results  The TgROP18 gene was about 1 665 bp in length and encoded for a protein of 544 amino acid residues and the former 47 amino acids consisted signal peptide sequences. PCR, enzyme digestion and DNA sequencing confirmed that the recombinant plasmid pET30a（+）-TgROP18 was constructed. Bacteria containing recombinant plasmid pET30a（+）-TgROP18 expressed a soluble protein of His-TgROP18 （Mr 59 800） after being induced with IPTG. His-TgROP18 reacted positively with mouse anti-T. gondii serum by Western blotting analysis.  Conclusion  The soluble His-TgROP18 protein shows certain immunoreactivity.

Key words: Toxophasma gondii, Rhoptry protein 18, Prokaryotic expression