Glutathione peroxidase (GPx) and glutathione reductase (GR) are key enzymes in the antioxidant defense systems of living organisms and protect organisms from environmental stresses. To investigate the mechanism of resistance to heat stress in the red alga Gracilaria lemaneiformis, the cDNA sequences encoding glutathione peroxidase and glutathione reductase of two strains (wild type and heat-tolerant cultivar 981) of G. lemaneiformis were successfully cloned using reverse transcription PCR and rapid amplification cDNA ends techniques. cDNA encoding GPx has 930 nucleotides with an open reading frame (ORF) of 750 nucleotides, encoding 249 amino acid residues. cDNA encoding GR was 1,572 nucleotides with a 1,416-nucleotide ORF encoding 471 amino acids. No introns existed in genomic DNA of GPx and GR of G. lemaneiformis. Southern blotting indicated that there was only one copy of GPx and GR in both strains. Under heat stress, bioactivity and mRNA transcription levels of both GPx and GR were upregulated in cultivar 981 compared to those in the wild type. These results indicate that both GPx and GR may play important roles in the ability of G. lemaneiformis to resist high temperatures.