Water level of the Tonle Sap is greatly influenced by the Mekong River. In order to detect landcover change in Tonle Sap floodplain, fifteen ALOS-PALSAR L-band data were acquired and examined from January 2007 to January 2009. Four methods applied to investigate the landcover change around the lake including grey difference images, correlation coefficient, texture feature difference images and multi-color composite images. Change maps of landcover (44 days interval) extracted from the difference images, coherence maps and texture feature difference images were formed. Two RGB images are also obtained by compositing three images acquired in early rainy season, in the middle of rainy season and at the end of the rainy season in 2007 and 2008. The results indicate that the change maps represent the relationship between vegetation and water level, leaf fall forest, cultivation and harvest crop.