The promoting effect of wood vinegar compounds on the fruiting of Pleurotus ostreatus (Japanese name, Hiratake) was investigated. Not only crude wood vinegar but its components, 3,5-dimethylphenol, 2-methoxyphenol, butanoic acid and 1-pentanol, had the ability to promote fruit-body formation on liquid medium. For use of these promoters industrially, a test for practical cultivation was carried out using a commercial sawdust medium. The addition of 100 μg/ml butanoic acid and 100 μg/ml 2-methoxyphenol into the sawdust medium after removal of the surface mycelial layer (kinkaki in Japanese) produced 29 and 23% higher yields of fruit-bodies than the control cultures (137.2g/bottle), respectively. The addition of the crude wood vinegar as a medium component into sawdust substrates in the concentration range of 0.1–6% increased yields of fruit-bodies by 21–42% over the control.