Antarctic marine organisms have developed in an environment of low temperatures and high levels of stability. Consequently, these species have lost the ability to adapt to sudden changes in temperature. Rising ocean temperatures could make the Antarctic sea urchin Sterechinus neumayeri vulnerable to pathogens, triggering responses that increase oxidative stress. In order to understand how the immune system reacts, we can analyze the expression of anti-oxidant molecules such as the peroxiredoxins (Prxs). Prxs are an anti-oxidant protein family with conserved catalytic redox-active cysteine residues. In S. neumayeri, one full-length cDNA of the gene that encodes Prx (Sn-Prx) was characterized. The Sn-Prx cDNA contains a 786-bp open reading frame, which encodes 262 amino acids, including two conserved cysteine residues that are characteristic of the typical 2-Cys subgroup of the Prx family. An in silico analysis was performed to establish epitope molecules, which were then chemically synthesized and used to obtain antibodies. The antibodies were validated by indirect ELISA against a synthetic peptide and western blot against S. neumayeri proteins. In different tissues, the expression of Sn-Prx protein was increased after Vibrio anguillarum challenge. Heat stress also increased expression of Sn-Prx in coelomocytes after 7 days, but the availability of the protein decreased in digestive gland tissues after 2 and 3 weeks of heat stress. This may indicate the involvement of Prx in antioxidant response in S. neumayeri. The evidence presented in this study proposes anti-Prx antibody as an experimental evaluation tool that can be used to establish a baseline of the ability of S. neumayeri antioxidant response.