Samar is one of the provinces in the Philippines with the most extensive remaining mangrove forest. However, information on ecology and carbon sequestration capacity is limited. Thus, this study aims to assess the species diversity, community structure, and carbon stock in the natural and planted mangrove stands in Zumarraga, Samar. The transect-line method was used to collect vegetation analysis and diversity data, while biomass estimation used an allometric equation. Fifteen sampling plots of 10 m x 10 m were established in each sampling site, representing the seaward, middleward, and landward zones. The species composition of these areas consists of 11 species belonging to 5 families. Biodiversity indices indicated very low species diversity for both types of mangrove forests. Avicennia marina was the most important species, with an importance value (IVI) of 168.55% (natural stand) and 75.61% (planted stand). The total carbon stock was 71.97 t C ha⁻¹ in the natural stand and 391.44 t C ha-1 in the planted stand. Overall, even if both mangrove stands have very low species diversity, their ability to store and sequester carbon cannot be undermined, as evident in the biomass and carbon stock values. Thus, sustainable management strategies and efforts should be made to protect this naturally grown and planted mangrove ecosystem.