Abstract: The objective of this study was to evaluate the molecular characteristics of heat shock protein 70 (HSP70) gene, and document changes in HSP70 gene expression upon exposure of Perinereis aibuhitensis to aqueous Cu²⁺. Full length cDNA of HSP70 was sequenced and the characteristics of the translated protein were determined and compared both with other ragworms species and other invertebrates. The results showed that the cDNA was 2161 bp and consisted of a 5′-terminal untranslated region (UTR) of 48 bp, a 3′-termianl UTR of 142 bp with a canonical polyadenylation signal sequence AATAAA and a poly A tail, and an open reading frame (ORF) of 1971 bp. The HSP70 protein was 656 amino acids with a calculated molecular weight of 71.43 kD and theore-tical isoelectric point of 5.15. Sequence analysis of the protein showed that HSP70 of P. aibuhitensis contained three signature sequences IDLGTTYS, IFDLGGGTFDVSIL and IVLVGGSTRIPKIQK all belonging to the HSP70 family, a cytoplasm characteristic motif of EEVD, and the C-terminal repeats of GGMP. The molecular characteristics of P. aibuhitensis shared 94% identity with other ragworms and 79% identity with other invertebrates. In ragworms exposed to Cu²⁺, expression of HSP70 mRNA increased significantly with Cu²⁺ concentration (0.2-5.0 mg·L^-1), and it reached the peak on 1-day exposure. In summary, the molecular characteristics of HSP70 of P. aibuhitensis were described, and its gene expression was inducible by exposure to aqueous Cu²⁺, suggesting HSP70 has potential to become a useful molecular biomarker of environmental pollution.