Abstract: The contents of nutrients and amino acids in the fruiting bodies of Agaricus bisporus cultivated on media containing rice straws, spent Pleurotus eryngii or spent Flammulina velutipe were determined. The nutritional values were analyzed by the internationally applied protein assessment method. The results showed that the medium formulated mainly with rice straws produced fruiting bodies with high crude protein (i.e., 40.00%) and fat (i.e., 3.20%) as well as a higher nutritional quality index than the media containing largely the spent mushroom materials. The amino acid ratios of the fruiting bodies indicated that A. bisporus harvested from the medium formulated with spent P. eryngii were nutritionally superior to the others. The spent mushrooms alsoproduced fruiting bodies with better amino acid composition than rice straws did. A pattern recognition analysis showed a closer resemblance of the proteins from the fruiting bodies of A. bisporus cultivated on medium consisted mainly of rice strawsor spent P. eryngii to those of eggs, at a score of 0.88, than that from the fruiting bodies of A. bisporus grown on medium of spent F. velutipe. In addition, the fruiting bodies contained more flavor amino acidswhen A. bisporus were cultivatedon media with the presence of spent mushroom substrates than rice straws. It appeared that medium formulations using spent mushrooms for A. bisporuscultivation could be furtherimproved to maximize the food quality of the fruiting bodies for consumption.