Hemocyanin is a copper-binding protein that plays a crucial role in the physiological processes of crustacean. In this study, the cDNA-encoding hemocyanin subunit , was cloned using expressed sequence tag (EST) analysis and a rapid amplification of cDNA ends (RACE) approach. The full-length cDNA of MnHc was 2 235 bp, consisting of a 5′ untranslated region of 10 bp, a 3′ untranslated region of 151 bp, and an open reading frame of 2 064 bp. The deduced protein had 688 amino acid residues with a molecular mass of 79.16 kD. Based on a protein similarity comparison, the two copper-binding sites and six histidine residues necessary for stabilization of oxygen-binding were highly conserved. Phylogenetic tree analysis indicated that Exopalaemon carinicauda. Quantitative real-time RT-PCR analysis showed that the gene was expressed in hemocytes, the hepatopancreas, muscles, testis and intestines, with the highest level of expression in the hepatopancreas and the lowest in muscles. After environmental hypoxia and reoxygenation challenge, the relative expression level of in the hepatopancreas was significantly higher compared with the control group at 12 h, 24 h post-hypoxia and 6 h reoxygenation, followed by a gradual recovery at 24 h reoxygenation. The highest titer of antiserum was up to 1120 000, as revealed by ELISA assay. The specificity of antibodies against hemocyanin was verified by westernblotting. The study indicates that the expression levels of in the hepatopancreasmay be affected by environmental dissolve oxygen, and hemocyanin may potentially be involved in the hypoxia stress response of .