Abstract: In order to obtain highly purified soft-shell turtle iridovirus(STIV) for immunological studies,3 methods were investigated.The purified virus was analyzed to certify its purity and protein structure.Results indicated an impurity and low recovery rate in the process applying two freezing-thawing cycles followed by differential centrifugation.Furthermore,the electron microscopic observation on the virus was difficult.On the other hand,by freezing-thawing the virus culture followed by magnetic stirring,ultrasonication and differential centrifugation,the virus recovery rate was improved.However,the virus structure was damaged.Alternatively,virus culture was concentrated by centrifugation,homogenization,magnetic stirring and differential centrifugation,in that order,and followed by sucrose density gradient centrifugation.The most satisfactory result was finally obtained.The virus particles collected could be observed in 30%-40%,40%-50% or 50%-60% sucrose density fractions.The most abundant and intact virions were seen in the 50%-60% fraction.The purified STIV virions were further subjected to SDS-PAGE.The result showed that the STIV contained more than 20 proteins,and that its major capsid protein corresponded to a 50kDa abundant protein.The Western-blot analysis further indicated that most of the protein bands could be specifically recognized by using high quality mouse anti-STIV serum.