Undergrowth communities in plantation forests are always synonymous with weeds which have long been seen as nuisance and harmful plants, especially in planted areas that are maintained. Understorey plays an important role as a source of organic matter, reducing the kinetic energy of rain and the forces of runoff over the soil, to prevent erosion by water. The mahogany tree (Swietenia mahagoni (L.) Jacq) is one of the choices of species used in government programs in the green revolution movement. It is possible that in the future there will be lots of mahogany plants around us. This study aims to analyze the types of understorey that exist in Mahogany Stands (Swietenia mahagoni (L.) Jacq) including Relative Density, Relative Frequency, Important Value Index, analyze the dominance index of understorey species in the stand Mahogany (Swietenia mahagoni (L.) Jacq), and analyzed the diversity and evenness of understorey species on Mahogany (Swietenia mahagoni (L.) Jacq) at KHDTK ULM which was the research location. The results of this study there are 16 species with a total of 384 types of undergrowth. The types obtained during data collection include alaban kapas, alang-alang, dambah, jawaling, juragi, karamunting, kopasanda, litu, madang pirawas, magatseh, mahang, pancing-pancing, papisangan, sarapangan, tampukas, tengkook ayam. The data from the calculation of understorey obtained the highest important value index of 49.48 from fishing rods, a dominance index of 0.13 which was included in the category of no dominant species, a diversity index of 2.26 which was included in the medium diversity category, and an evenness index of 0.38 which is included in the category of medium equity.