Calreticulin (CRT) is a multifunctional and highly conserved Ca2+-binding protein shared among vertebrates and invertebrates. In this study, we cloned and characterized a CRT gene, PyCRT, from Yesso scallop, Patinopecten yessoensis. The full-length cDNA of PyCRT was 1830 bp, including a 1242 bp open reading frame (ORF), a 29 bp 5′-untranslated region and a 559 bp 3′-untranslated region. PyCRT was consisted of three distinct structural and functional domains (N-, P- and C-domains), a signal peptide and an endoplasmic reticulum (ER) retrieval signal sequence (HDEL). Tissue specific expression analysis showed that PyCRT was distributed widely in Yesso scallop, and was highly expressed in the mantle and hemocytes. After Vibrio anguillarum challenge, the expression of PyCRT in hemocytes had a significant increase and reached the maximum level at 12 h post-infection. We also demonstrated for the first time in mollusc that the recombinant PyCRT (rPyCRT) could bind to the Gram-negative bacterium V. anguillarum, Escherichia coli and the Gram-positive bacterium Staphylococcus aureus. Our results suggested that the CRT gene from Yesso scallop possessed immune-related regulatory functions in the innate immune system in scallops.