Abstract: In view of the issue of mangrove resources protection in Kra Isthmus, we have monitored and analyzed the changes of the mangrove resources in the eastern and western coastal, using the data of Landsat, HJ-1B and SRTM and taking the Maximum likelihood method. The results indicate that:(1) The mangrove in the western coastal of Kra Isthsums have a wide distribution and large area. While, they have less, centralized distribution and small area in the eastern coastal. (2) In recent 40 years, the areas of the mangrove have reduced in general. In contrast with western coastal, the area of eastern coastal have decreased dramatically. However, the large amount of reducing allconcentrated in a certain period of time from 1989 to 2001. (3) The main influence factors that causing the changes were different in the eastern and western coastal. In the eastern coastal, the excessive building of shrimp ponds is the major reason; but the expansion of urbanization and coastal exploitation are the main cause in the western coastal.