The ostracode foraminifera microbiogenic sediments of the Nagdon Estuary, which is a deltaic, have been analysed. Twenty four species representing seventeen genera of ostracodes and some species representing twenty three genera of foraminifera are identified and counted. From these data their geographical distribution patterns aree obtained and biotopes are determined in relation to the sediment distribution and hydrological parameters. There are several tendencies in the distribution of ostracodes and foraminifera. Both ostracode and foraminiferall population increased seaward. The ratio of foraminiferal population to the sum of the ostracode and the foraminiferal population, as well as the ratio of calcareous foraminifera to the sum of calcareous and agglutinated foraminiferal population, also increased seaward. The biotopes can be divided into two. Biotope I is the innershore environment and Biotope II offshore environment.