Ecological study of Gigantochloa manggong, one of the endemic bamboo species at Java was done inthe secondary tropical forest of Meru Betiri National Park, East Java, Indonesia. Distribution was limit-ed in eastern part of the national park. In general, G. manggonggrows well in lowland secondary forestpatches at altitudes 5 - 50 m on the clay loam soil. Absence of large trees caused canopy gaps whichmade bamboo grows well and spread. There were several associate species such as Callamussp.,Erioglussum rubiginosum, Voacanga grandifolia, Pleomelesp., and Ficussp. Throughout the fieldobservation, its sexual reproduction was not found. However, vegetative reproduction by developingnew culms was found in all of the quadrats. Bamboo harvesting in Sukamade forest by villagers was thethreats of G. manggongpopulation at the wild habitat. Furthermore, our study showed that the range ofthe species distribution has contracted substantially from that recorded in 1987, and this has led to itsassessment as an endangered species. Unsustainable exploitation and habitat loss might be importantfactors toward the extinction of G. manggongin the natural habitat.