Total protein content and level of 14 amino acid in mature acorns of 20 Quercus taxa from Turkey were studied. The range of total protein amounts between 2.75 and 8.44% were detected among taxa. Similar values in related species and variety level were observed. The amino acid profiles for each taxon were characteristically different and high variability of individual amino acid concentration was present at variety, subspecies and species levels. Different amino acid concentrations, relative percentages and critical values of some amino acids are thought to be additional considerable parameters for diagnosis of Quercus. Generally higher total quantity of amino acids in section Quercus and lower values in section Ilex were observed. When the essential and non-essential amino acids are expressed as a relative percent of total protein indicating quality of proteins, the ratios varied significantly among taxa (p < 0.05). But, no significant difference at section level were detected. Major amino acids were aspartic acid and glutamic acid showing the largest variations and the lowest levels were detected for methionine. Amino acid concentrations ranged from 1665 for aspartic acid to 13 mg/100 g dry wt. for methionine. All taxa had relatively higher amounts of leucin, lysin and valine than other essential amino acids. The highest quantity of protein and amino acids was recorded for Q. infectoria ssp. boissieri and the lowest for Q. pontica. The level of all essential amino acids in examined taxa was not sufficient compared to FAO scoring pattern for children (1985). But, threonine and valine in Q. infectoria ssp. boissieri and isoleucine in Q. petraea ssp. iberica show remarkable concentrations to the requirements. All examined essential amino acids among taxa generally provide adequate levels for adults according to FAO standard.