A rapid, precise, and dependable method for quantifying flavonoids in the fruiting bodies of was established using ultra-high-performance liquid chromatography coupled with triple quadrupole mass spectrometry (UHPLC-QQQ-MS/MS). Separation was achieved using a ZORBAX Eclipse Plus C18 column (1.8 μm, 3.0 mm × 100 mm) with a 15 min gradient of a mobile phase consisting of 0.01% aqueous formic acid and 2 mm/L ammonium formate (mobile phase A), and 0.01% formic acid and 2 mm/L ammonium formate in methanol (mobile phase B). A mass spectrometry analysis was performed using the multiple reaction monitoring (MRM) mode with an electrospray ion source. This method enabled the simultaneous detection of 10 flavonoids (sakuranetin, quercitrin, myricitrin, kaempferol, luteolin, rutin, hyperoside, kaempferol-3--rutinoside, catechin, and catechin gallate) in the fruiting bodies of . Additionally, we applied this method to analyze the flavonoid content in fruiting bodies of various species. The results revealed substantial variations in flavonoid content, up to a 100-fold difference, among different species, with myricitrin, hyperoside, and rutin identified as the most abundant flavonoids. This protocol serves as a valuable tool for quantifying flavonoid compounds in different species or under diverse cultivation conditions, particularly for identifying species with high levels of specific flavonoid compounds.