This invention relates to a method for producing γ -aminobutyric acid, and in particular, to a method for producing γ-aminobutyric acid with Antrodia camphorate mycilium or Antrodia cinnamomea mycilium, a kind of fungi, which grow in inner side of Cinnamomum kanehirae, a kind of tree, which is only seen in Taiwan. The method includes cultivating Antrodia camphorate mycilium with liquid fermentation culture; isolating and drying Antrodia camphorate mycilium; then extracting with aqueous or organic solvent in order to obtain a substance comprising γ-aminobutyric acid. The invention also relates to a material composed of said substance and a medicine or food acceptable adjuvant, diluent or excipient
