Subaqueous sedimentological studies were carried out in the Khlong Thom and Satun areas, South Thailand where mangrove habitats are widely distributed, for the purpose to illustrate present subaqueous sedimentary processes around the habitats. Water areas in both are sedimen-tologically defined as tidal current dominated estuarine environments. Fifty-six subaqueous sediments from the Khlong Thom area and 53 from the Satun area were obtained and sedimentologically analysed to comprehend their textural and compositional features, and their spatial distributions. Water depth and surface water chemical properties of measurements were conduced in both areas to grasp subaqueous topographies and saline!fresh water mixing processes, respectively. A clear decrease of salinity is recognized from the Straits of Malacca area to the innermost parts in both areas, and no marked trend of it is detected between surface and bottom waters. Sandy sediments mostly cover the bottom surface of the Khlong Thom area, while muddy sediments dominate in the Satun area. The difference between them are resulted mainly from the difference of their geological settings. Sandy terrigeneous sediments consisting mainly of quartz in the bottom sediments from both areas are derived mainly from the consolidated strata cropping mainly out in the inner parts in both areas, but such micro-organic remains as benthic foraminifers and marine ostracodes are originated in the area of the Straits of Malacca. Further, charcoals derived only from villages and kilns in and around the mangrove habitats are dominant in the sediments from the inner parts. Because of these sediments are traceable wholly or partly in the bottom sediments and they indicate certain and relative source areas, course ways of subaqueous sediment transportation by tidal currents in both areas are inferred on the basis mainly of their spatial distribution of grain-sizes and relative amounts.