Two varieties of Pleurotus sajor-caju, obtained from the wild and cultivated (on shredded corncobs) were separated into cap and stalk and analysed on dry weight basis. The proximate composition (g/100 g) showed that both varieties were highly concentrated in crude protein. The cultivated cap (Cc) was found to accumulate higher concentration of crude protein (26.34%) and ash (10.37%) than the wild cap (Wc), which had higher crude fat (3.90%) and crude fibre (16.32%) concentrations while the wild stalk (Ws) contained the highest concentration of crude fibre (26.14%). Amino acid analysis showed the mushroom protein to be a rich source of nutritionally useful essential amino acids with leucine as the most abundant occurring in highest concentration (mg/g) in the Cc (64.8 +/- 0.24). Methionine and cysteine concentrations were low as confirmed by their chemical scores (0.29-0.59). There was a significant difference (P<0.05) in the distribution of amino acids in the mushroom varieties and parts. The total essential amino acid (TEAA) in the cultivated range between 42.91-43.69% while in the wild it was between 42.90-43.73 % of the total amino acid content. The amino acid concentration was a function of mushroom variety and part selected.