<p>Mangrove ecosystems play an important role in carbon sequestration and climate change mitigation; however, empirical data from small-island regions such as Timor-Leste remain limited. This study quantified mangrove biomass and carbon stocks in the Sabuli mangrove ecosystem, Metinaro, Timor-Leste, using a non-destructive field-based approach combined with allometric modelling. A total of 109 mangrove trees across 13 sampling plots were measured, including diameter at breast height (DBH), tree height, and species composition. Mean above-ground biomass (AGB) was estimated at 35 t ha⁻¹, while below-ground biomass (BGB) reached 13 t ha⁻¹, resulting in a mean total biomass (TB) of 48 t ha⁻¹. Estimated carbon stock averaged 23 t C ha⁻¹, equivalent to 84 t CO₂e ha⁻¹. Vegetation structure exhibited substantial variability in DBH and tree height, indicating heterogeneous stand conditions and multiple growth stages. Species composition was dominated by Sonneratia alba, Rhizophora apiculata, and Ceriops tagal, with Sonneratia alba contributing the largest proportion of biomass. Biomass distribution showed moderate variation across seaward, middle, and landward zones, without a clear zonal gradient. Instead, biomass accumulation was primarily associated with stand structure and the occurrence of large-diameter trees. These findings provide the first field-based baseline dataset for mangrove biomass and carbon storage in Timor-Leste and contribute to blue carbon assessment, climate mitigation planning, and sustainable mangrove management in small-island coastal systems.</p>