Sudoite, an aluminium-rich di-trioctahedral chlorite, is known primarily from high-grade diagenetic/low-temperature metamorphic Al-rich rocks and from hydrothermal deposits in Al-rich terrains. This contribution reports a rare occurrence of pore-lining sudoite in Permian red beds from the eastern part of the Southern Permian Basin. Sudoite is a ubiquitous mineral in aeolian sandstones of the Eastern Erg, a large dune field buried in the subsurface of the Fore-Sudetic Monocline, SW Poland. Sudoite crystals are arranged in a honeycomb texture and often associated with high-porosity intervals. It is concluded that sudoite crystallized at the expense of early diagenetic dioctahedral smectite at a temperature lower than 180°C under the influence of hot, Mg-rich and K-poor fluids, which migrated from a basement and/or deep part of the basin upward through permeable aeolian sandstones and mixed with colder pore solutions. Tosudite was a likely intermediate phase in the smectite to sudoite conversion.