[en] An investigation was conducted to assess the ability of three species of brown-rot fungi to decolorize and transform methyl orange dye. Methyl orange was decolorized in a potato dextrose agar medium by Fomitopsis pinicola, Gloeophyllum trabeum, and Daedalea dickinsii at different concentrations of 50, 75, and 100 mg L⁻¹. Based on the values of the decolorization index, the highest methyl orange decolorization was found approximately 91% by F. pinicola, followed by D. dickinsii and G. trabeum of 82% and 76%, respectively, at a concentration of 50 mg L⁻¹. F. pinicola had the highest methyl orange transformation with percent decolorization values of approximately 97%, followed by D. dickinsii and G. trabeum of 93% and 67%, respectively, after a 14-day incubation period in potato dextrose broth. F. pinicola transformed methyl orange into six metabolic products: compounds 3, 6, 7, 8, 9, and 10, while G. trabeum transformed methyl orange into five metabolic products: compounds 1, 2, 3, 4, and 5. Among brown-rot fungi, D. dickinsii had more metabolic products, with compounds 3, 4, 6, 11, 12, 13, 14, 15, 16, 17, and 18. Based on the identification of metabolic products, novel bio-transformation was proposed that brown-rot fungi initially transformed methyl orange via three pathways: (1) demethylation, (2) desulfonylation, and (3) hydroxylation. This study indicated that brown-rot fungi can be used to decolorize and transform methyl orange dye as well as proposed novel bio-transformation of methyl orange by brown-rot fungi.