As the importance of public health increases with the spread of infectious diseases, functionality has become a factor affecting consumers’ purchase of mushrooms. Therefore, the bioactive components of button mushrooms (Agaricus bisporus), which are generally known to promote button mushroom consumption, were analyzed. White and brown button mushrooms were compared and white beech mushroom (Hypsizygus marmoreus) were used as a control. White button mushrooms had higher sugar and inorganic potassium concentrations than brown button mushrooms, whereas sodium, magnesium, and vitamin C concentrations were not significantly different between the different button mushrooms. Moreover, there was approximately twice as much ergosterol in white button mushrooms than brown button mushrooms. Brown button mushrooms had higher concentrations of β-glucan and oxalic acid than white button mushrooms, but there was no significant difference in total organic acid content between the two mushroom types. High concentrations of the essential amino acids, ergothioneine, isoleucine, and leucine and the non-essential amino acids, glycine and alanine, were observed. Concentrations of the vitamin B group and total polyphenols were also high.