Lowland tropical rainforests are rich in biodiversity and maintain stable ecosystems. However, disturbances such as fires, natural disasters, and unsustainable logging can disrupt this stability. In Lamandau Regency, Central Kalimantan, the potential for forestry development is substantial, necessitating proper planning and implementation. This study aims to evaluate the structure, composition, biomass potential, and carbon content of forests in Benyawai and Salajaan Hills, which are proposed as Great Forest Parks (Tahura). These forests play a crucial role in supporting biodiversity, ecosystem preservation, and carbon sequestration. Research was conducted in July 2022, utilizing representative plots of 1 hectare each. The study area has a humid tropical climate with significant rainfall and diverse soil types. The research involved measuring tree diameters, heights, and species identification. Dominant species were determined based on importance value indices, and biomass and carbon content were calculated using established equations. The results showed a high species diversity with 58 species in Benyawai Hill and 47 in Salajaan Hill. Dominant species such as Ilex cymosa and Shorea laevis were identified. The forest stands displayed an inverted “J” curve typical of healthy forests, with a higher number of smaller diameter trees. Regeneration was evident, with species like Ilex cymosa and Shorea laevis present in all strata from seedlings to mature trees. Biomass and carbon content were significant, highlighting the forests’ potential in carbon sequestration. Proper management of these forests is essential for maintaining their role in mitigating climate change through CO2 absorption. This study provides baseline data crucial for future forest conservation and carbon trading regulations.