The brown-rot fungi play an important role in forest ecosystems; they can degrade celluloses and hemicelluloses of wood and maintain nutrient cycling. Some of the brown-rot fungi also have important economic value as medicinal or edible mushrooms. Recent studies showed that the ability to produce brown rot has evolved independently at least five times. Nevertheless, the Polyporales contains the vast majority of the species of the brown-rot fungi. In this study, the classification system of the brown-rot fungi within the Polyporales is revised. Furthermore, the phylogenetic relationships of brown-rot fungi within the Polyporales are analysed based on DNA sequences of multiple loci including the internal transcribed spacer (ITS) regions, the large subunit nuclear ribosomal RNA gene (nLSU), the small subunit nuclear ribosomal RNA gene (nSSU), the small subunit mitochondrial rRNA gene sequences (mtSSU), the translation elongation factor 1-α gene (TEF1), the RNA polymerase II largest subunit (RPB1) and the second subunit of RNA polymerase II (RPB2). The study showed that the brown-rot fungi within the Polyporales formed fourteen lineages, which are assigned at family level, including four new families: Auriporiaceae, Piptoporellaceae, Postiaceae, Taiwanofungaceae, and ten existing families: Adustoporiaceae, Dacryobolaceae, Fibroporiaceae, Fomitopsidaceae, Laetiporaceae, Laricifomitaceae, Phaeolaceae, Pycnoporellaceae, Sarcoporiaceae, and Sparassidaceae. Meanwhile, eleven new genera, viz., Austroporia, Aurantipostia, Austropostia, Daedalella, Nothofagiporus, Pseudoantrodia, Pseudofomitopsis, Rhodoantrodia, Tenuipostia, Wolfiporiella and Wolfiporiopsis are proposed; eighteen new species, viz., Amyloporia nivea, Antrodia subheteromorpha, Aurantipostia macrospora, Austropostia hirsuta, A. plumbea, A. subpunctata, Cystidiopostia subhibernica, Daedalella micropora, Fuscopostia subfragilis, Lentoporia subcarbonica, Melanoporia tropica, Neolentiporus tropicus, Phaeolus fragilis, Postia crassicontexta, Pseudoantrodia monomitica, Pseudofomitopsis microcarpa, Resinoporia luteola and Rhodonia subrancida are described; and twelve new combinations, viz., Austroporia stratosa, Austropostia brunnea, A. pelliculosa, A. punctata, Nothofagiporus venatus, Rhodoantrodia tropica, R. yunnanensis, Tenuipostia dissecta, Wolfiporiella cartilaginea, W. curvispora, W. dilatohypha and Wolfiporiopsis castanopsidis, are proposed. Illustrated descriptions of the new species are provided. Notes on the genera of brown-rot fungi within the Polyporales are provided.