Dahlia mosaic virus (DMV) is the causal agent of one of the most important diseases of Dahlia pinnata. The nucleotide sequence of a 1,195-bp fragment of its genome was amplified and characterized. Based on this sequence, polymerase chain reaction (PCR) assays were developed for detection of DMV. The nucleotide sequence confirmed the classification of DMV as a member of genus Caulimovirus since it was similar to a region covering partly open reading frames (ORFs) IV and V found in caulimoviruses. The two most closely related viruses on the basis of comparison of ORF V fragments were shown to be Figwort mosaic virus and Mirabilis mosaic virus with 66.6 and 68.1% identity, respectively. Two PCR assays were developed using identical primer pairs: a real-time PCR based on SYBR green chemistry and a conventional PCR. Both methods clearly discriminated DMV-infected and healthy dahlia. The real-time PCR assay detected DMV-infected material that was diluted 105-fold in healthy material.