We examine the southern Vietnamese site of Rach Nui, dated to between 3390 and 3850 cal BP, in the context of three major aspects of the Neolithic in Mainland Southeast Asia: mound formation and chronology, construction techniques, and subsistence economy. Results indicate that this ca. 75 m in diameter, 5 m high mound, comprising over a dozen phases of earthen platforms, upon which were raised sophisticated wooden structures, was built in <200 years. While consuming domesticated millet, rice, and occasionally dogs and pigs, the main subsistence orientation included managed tubers and fruits and a range of mangrove ecosystem taxa: catfishes, turtles, crocodiles, monitor lizards, macaques and langurs, to name a few. This combined vegeculture-foraging lifeway in a mangrove forested environment, likely in the context of a tradable goods extractive industry, adds to a growing picture of significant diversity, and sophisticated construction skills in the Southeast Asian Neolithic.