ABSTRACT: Anew species of Reophax is documented from the shallow marine settings offshore Brunei Darussalam. The new taxon differs from other recent species of Reophax by its selective agglutination consisting mainly of tests of megalospheric specimens of Amphistegina. Reophax bruneiensis n.sp. differs from other known species in having a selectively agglutinated wall, few numbers of chambers increasing rapidly in size, and a terminal aperture not supported by any neck. This new species possibly acts as detritivore within the bottom sediments characterized by differentiated calcareous bioclasts and clay-sized siliciclasts derived by the river supply.