The effect of spatial change on the coastal area affected the status of mangrove forest. Richness of mangrove forest of Prasae estuary has been changed over time due to human activities. This research aimed to use remote sensing technology to investigate the richness of the mangrove forest in the coastal of Prasae estuary in years 2009, 2014, and 2019. Four sub-districts of Klang district, Rayong province were analyzed; namely Paknam Krasae, Pang Rad, Nern Koh, and Klong Pun. Normalized Difference Vegetation Index was evaluated for indicated of biomass that covers land area. The results showed that overall accuracy each year was 80.56, 79.17, and 82.64 %, respectively. The areas of mangrove forest in 2009, 2014, and 2019 were 11,316.48, 18,058.19, and 10,060.86, rai respectively. The prediction of the mangrove forest areas using CA-Markov model indicated that the mangrove area in 2029 would be 7,662.14 rai, which approximately decreases for 23 %