The DNA fragment encoding salmon calcitonin was separated from the salmon DNA with PCR method. It was recombined into the fusion expression vector (pGEX-2T) which included a Glutathion-S-Transferase (GST) gene and was transformed into E. coli JM109 and then expression was induced with IPTG. The fusion protein (GST-sCT) accounted for 38%-40% of the total cellular protein and was purified from the soluble expression products by glutathion sepharose 4B affinity chromatography. The purity of GST-sCT is about 80% and it showed a positive immunological reaction in calcitonin enzyme immunoassay.