We investigated 18 amino acid contents in the fruiting bodies of Agaricus strains to understand their variation in the harvesting periods. Total content of amino acid was different depending on the isolates. In the case of A. bitorquis and A. brunnescens, the total amino acid content increased and correlated with the harvesting periods. For commercial strains of A. bisporus, such as Yangsongi-505, Yangsongi-705 and commercial strain A collected in the market, it increased until the second harvesting period, but decreased in the third harvesting period indicating that these three isolates exhibit the exceptions for the general trend. Among isolates we used in our experiments, the isolate of A. brunnescens contained the highest and two isolates of A. bisporus were the lowest in total amino acids. We found two trends for the contents of each amino acid in the fruiting bodies of Agaricus spp.. One is the same with the trend of the total amino acid content and the amino acid content were largely correlated with the harvesting period. The other is the trend of increase of amino acid until the second harvesting period and decrease of amino acid in the third harvesting period, which was also shown in the total amino acid content of A. bisporus. Generally, the most amino acid contained in Agaricus was cysteine and followed by phenylalanine, glutamic acid, lysine, proline and histidine.