A disorder was recently observed in a 76-year-old Japanese beech (Fagus crenata) bonsai with symptoms including marginal scorch of leaves bordered by a chlorotic halo, as well as a premature leaf browning and defoliation. Leaf midrib extracts from the affected bonsai reacted with an antiserum specific to Xylella fastidiosa in an enzyme-linked immunosorbent assay. When the total DNA from the leaf midribs of the affected bonsai was extracted and subjected to polymerase chain reaction (PCR) with primers specific to X. fastidiosa, a 472-bp PCR product was detected. The PCR product was confirmed to be the predicted X. fastidiosa product by sequencing and sequence comparison with the reported genomic sequence of X. fastidiosa. Enzyme-linked immunosorbent and PCR assays of leaf midrib extracts of a symptomless Japanese beech tree were negative. This is the first report of X. fastidiosa associated with leaf scorch in high-valued bonsai and in beech.