To infer phylogenetic relationships between species of Trichaptum (Polyporaceae), RFLP analyses of PCR-amplified DNAs were accomplished. Regions coding for ITSs of nuclear SSU rRNA genes and for mitochondrial SSU rRNA genes from thirteen strains of four Trichaptum species (T. abietinum, T. biforme, T. fusco-violaceum, and T. laricinum) were amplified and digested with eight restriction enzymes. All the fragmentation patterns were characterized and coded as 0/1 for the absence/presence of fragments. A phylogenetic tree based on the combined data sets was constructed using the Dollo parsimony method. While every two strains of T. abietinum, T. biforme, T. fusco-violaceum, and T. laricinum formed an independent group, the other strains of T. abietimum and T. fusco-violaceum made mixed groupings among compared strains. It is inferred that T. abietinum and T. fusco-violaceum have more variations, possibly geographic or physiological ones, than other species in the genus.