Microfaunas of borehole PRD16 in the Pearl River Delta have been quantitatively analyzed in this paper. A total of 24 benthic foraminifera species referred to 12 genera and 13 ostracod species referred to 9 genera were found in the borehole. They can be divided into 3 ecological groups. The microfaunal analytical results, combined with lithological and sedimentary grain characteristics, suggest that the study area experienced environmental changes since the Late Pleistocene. A riverine environment began to develop before 34 600 cal a BP. Between 34 600 and 23 900 cal a BP, the environment generally changed to an estuarine condition. Between 23 900 and 7 960 cal a BP, the sediments experienced weathering and erosion, characterized by a layer of mottled clay. At around 7 960 cal a BP, sea level rose rapidly and an estuary environment with euryhaline foraminifera and brackish ostracod faunas existed until 2 810 cal a BP. Two secondorder sea level fluctuations can be recognized based on the composition and abundance of microfaunas. The maximum water depth occurred at approximately 3 873 cal a BP, demonstrated by the highest abundance of foraminifera and ostracods in the borehole. Since 2 810 cal a BP, the environment gradually changed into a fluvial supratidal zone with increased influence of river processes.