The gene of nonstructural protein 9 of SARS-coronavirus(SARS-CoV) was amplified using PCR from the product derivated from reverse transcription of SARS-CoV genome RNA,and was inserted into the multiple cloning sites of the expression vector pGEX-6p-1.Recombinant strain induced with IPTG expressed the specific soluble protein.The nsp9 protein was harvested and purified by affinity chromatography and processed by prescission protease.Polyclonal serum against the nsp9 protein was raised in rabbit.