Uracil auxotroph of Pleurotus ostreatus was transformed to prototrophy by means of particle bombardment. Five transformants were obtained under three conditions differing in the two parameters of target distance and helium pressure. The transformation frequency was one transformant per μg of DNA. In the transformants, plasmid DNAs were integrated into the genomic DNA and stably maintained. This is the first report on transformation of P. ostreatus by particle bombardment.