Mangroves appear along deltaic and estuarine coastlines and in more sheltered areas. There are three important factors related to the response of the mangrove ecosystem to natural and anthropogenic impacts: accumulation speed of sediments, erosion speed and possibility to deeply enter to inlands in the case of coastline erosions (Woodroffe. 1992). The presentation outlines some results from studies of sediment dynamics in mangrove areas, Ho Chi Minh - Dong Nai river delta (Can Gio biosphere reserve) and Mekong river (Bo De estuary), in Southern Viet Nam.