Pleurotus cornucopiae (PC) mushrooms is found in the field and commonly known in Japan as Tamogidake mushrooms. Recently it has been reported that PC also alleviating the toxicity of heavy metals. However little is known about mechanism of the action of PC on osteoblast differentiation, especially in transcription factor. Inhibitor of DNA binding-1 (Id-1) function has been linked to the proliferation, migration, and senescence of cells, and studies about relationship between Id-1 and biological function. Therefore, this study was aimed to investigate the effect of PC on osteoblast differentiation and expression of Id-1 and Id-2. PC treatment increased ALP, Col 1 and OCN. PC treatment up-regulated the mRNA levels of Id-1 and Id-2 genes. This PC–induced osteoblast differentiation is more effective in lower doses rather than high doses. This study shows that expression of Id-1 and Id-2 was increased in a dose-dependent manner during PC-induced osteoblast differentiation.