Mangrove forests are the main carbon absorption and sequestration source, serving as a typical ecosystem in coastal areas. Despite numerous studies on temporal changes in carbon storage, there is limited information on the examination of gross primary productivity (GPP) in mangrove forests. GPP is the overall quantity of organic matter produced in the vegetation through photosynthesis, including the portion used for respiration. In the context of global warming and climate change, GPP is frequently used as an indicator of the total amount of carbon dioxide (CO₂) assimilated by the ecosystem, particularly vegetation. The advancement of geographic information systems (GIS) and remote sensing methods has enabled the estimation of GPP rates on a spatial-temporal basis. Therefore, this study aimed to estimate and explore the relationship between GPP and vegetation density in the mangrove forest of Ujung Pangkah, Indonesia. Multi-temporal Sentinel-2 image data from 2018 to 2022 were used for analysis, while the Vegetation Production Model (VPM) was applied to calculate GPP. The results showed a steady increase in average GPP from 1997.91 grC m^-2 yr^-1 in 2018 to 2290.09 grC m^-2 yr^-1 in 2022. The increase showed significant improvement in the condition of the Ujung Pangkah mangrove forest. This was further confirmed by the strong relationship between GPP and the Normalized Difference Vegetation Index (NDVI), which was used to determine vegetation density (R²>0.9, p<0.05).