Brunei Darussalam’s geology is characterized by extensive Neogene fluvio-deltaic to shallow marine siliciclastic deposits, which have been studied here to highlight their palynological content. So far, there are only few reports that investigate fossil pollen and only one focuses on detailed taxonomical description using light microscopy (LM). The rest are studies on a wider regional scale in northwest Borneo sometimes including Brunei but without much emphasizes on taxonomy. To investigate pollen thoroughly, the use of scanning electron microscopy (SEM) is important, as this can provide valuable information on the sculptures of the pollen grains which with LM alone cannot be observed. Our study here provides LM images alongside the first SEM images of pollen and spores from Miocene sediments in Brunei Darussalam. The results point to a moderate-diverse flora comprising 37 families and 62 pollen and spore taxa. Most common ones are mangrove types which are Rhizophoraceae and Lythraceae taxa. The families of Combretaceae, Malvaceae, and other less common pollen groups are typical of tropical floral elements. The recovered families of Anacardiaceae, Arecaceae (five taxa), Calophyllaceae, Dilleniaceae, Dipterocarpaceae (two taxa), Elaeocarpaceae, Euphorbiaceae (four taxa), Phyllanthaceae (two taxa), Podocarpaceae, Proteaceae, Rubiaceae, Sapindaceae and Sapotaceae indicate mixed Dipterocarpaceae forests ranging from hinterland to peat swamp areas.