Mangroves are unique tropical coastal wetland ecosystems that have important roles to climate change adaptation and mitigation. Recent studies showed that mangroves have been severely threatened by deforestation, land use change, aquaculture and other human activities. This study shows that remote sensing techniques can assess the spatial extent and aboveground biomass spatial data of mangrove ecosystems in Segara Anakan lagoon, southern coast of Central Java Province. By combining Landsat 7 ETM+ satellite and aboveground biomass field data in 2009 there was increasing pattern of aboveground biomass with mean value of 359 Mg ha-1 and 547 Mg ha-1 for 2001 and 2013 respectively. The increasing biomass value implies that mangrove ecosystems in this lagoon could survive and grew well although severely threatened due to mangrove conversion. Despite of some limitation data availability and processes, this study fills the gap information on aboveground biomass mapping and may be very valuable to support monitoring on deforestation and degradation and other activities like measuring, reporting, and verification (MRV) of carbon stocks and reducing emission from deforestation and degradation (REDD+) especially on coastal mangrove forests.