The research applied immunohistochemistry technique to diagnosis of classical swine fever (CSF) in pigs. Ten pigs with clinical sign of CSF were necropsied for taking samples to serve for this study. The results showed that ten pigs were positive for classical swine fever virus, in which the positive rate of tonsils, spleen and lymph nodes in mesentery were 100 percent
in small intestine and liver were 80 percent, another tissues had lower positive rate and lowest positive rate in the colon were only 30 percent. The results of this research indicated that tonsils, spleen, lymph nodes in mesentery were exact for diagnosing by immunohistochemistry and useful for isolating virus from field.