Abstract: Glutathione peroxidase (GPx) has been widely used as a biomarker of environmental stress in ecotoxicology. In this present study, GPx gene in Euplotes vannus was cloned and characterized. Degenerate primers were designed according to the glutathione peroxidase　amino acid sequences in conservative area from similar species. The ful-length cDNA was cloned from　E. vannus using RACE-PCR. Results showed that the complete cDNA in E. vannus is 672bp encoding 182 amino acids and belongs to thioredoxin-like superfamily. Analyses of the derived amino acid sequence data showed that GPx protein contains conservative structure, such as conserved catalytic residues and characteristic motifs, which is typical of glutathione peroxidaseas. Phylogenic analysis of amino acid sequences showed that E. vannus shares higher homology and nearer affinity with other ciliate species.