The molecular phylogeny of the long-horned beetle tribe Lamiini Mulsant (Coleoptera: Cerambycidae) in Japan (12 genera, 25 species, 3 additional subspecies) was determined based on mitochondrial 16S rRNA and cytochrome oxydase subunit I. The monophyly of the tribe Lamiini was supported, whereas that of the genus Acalolepta Pascoe was unclear. Evolution of host plant use in Lamiini was estimated using the molecular phylogeny. For adult and larval host plant kind-and-condition, the most ancestral state was for weakened to dead broad-leaved trees, whereas derived states favored conifers, healthy broad-leaved trees, and herbs. For adult and larval host range, the most ancestral state was polyphagy, whereas oligophagy and monophagy were derived. Evolution of hosts' idiosyncrasy and that of the insects' host range were related in many lineages. Our results partly support the hypothesis that habitation in living trees requires dietary specialization in phytophagous insects.