The classical swine fever viruses(CSFV)in Taiwan collected from 1989 to 2003 have been investigated retrospectively by Pan (2005). It described that new CSFV strains, which included genetic type 2.1a, 2.1b and 2.2 of CSFV, invade into Taiwan after 1994. However, those strains cannot be typed genetically at that time. Therefore, a new diagnostic technique for rapidly, sensitively, specifically, and differentiating genetic types of CSFV is necessary. The aim of our study is to develop a diagnostic technique on the multiplex real-time PCR. The multiplex real-time PCR includes a pair of universal primers and several specific probes. The new diagnostic technique could detect new CSFV strains invading into Taiwan and shorten the time of diagnosis on the chronic CSF.