The objective of this study was to investigate the amino acid composition and antioxidant properties of two oyster mushroom species, Pleurotus ostreatus and Pleurotus sajor-caju, commercially cultivated in NE Thailand.Proximate composition and dietary fibre of dried mushrooms were determined.Amino acid composition of fresh mushrooms was analysed by HPLC. Water and ethanol extracts were obtained from dried mushrooms and determined for total phenolic contents (TPC) by the Folin-Ciocalteu method, free radical scavenging efficacy by the DPPH method, and reducing power by the ferric reducing-antioxidant power method.Except for protein, proximate compositions of dried mushrooms were significantly different. Similar amino acid profiles in both mushrooms were obtained, with glutamic acid, aspartic acid, and arginine being the three most abundant.