Classical swine fever virus (CSFV) is the most insidious and devastating viral pathogen of pigs in Taiwan. The lapinized live vaccine (LPC) has been used to control the diseases since 1950s. However, the outbreaks of endemic continuously occurred in every year. We consider that the approaches of diseases control must be based on detailed knowledge of virus biology. Previous studies have indicated that some of the viruses containing the positive-strand of RNA genome could be manipulate with their full-length cDNA in a plasmid. Construction of the full-length genome in a plasmid is therefore required for the studies of viral virulence and their characters. To develope reverse-genetic systems for studying the molecular biology of the virus, we first will construct a plasmid containing the entire genome of CSFV cloned as cDNA. Viral cDNAs were amplified from viral RNA genome with RT-PCR and ligated into a full-length in a plasmid. The chimeric plasmid will be transfected into PK-15 cells to produce the infectious CSFV. This result will define the functional open reading frame, 5' and 3'-termini in viral genomic RNA. Immediate applications of this system will include development of safe and effective live vaccine strains possessing predetermined attenuating mutations.