The new mangrove barnacle, Fistulobalanus sumbawaensis sp. nov. from Sumbawa Island, Indonesia shares the common morphological characteristics with the subfamily Amphibalaninae in having a shell wall of six, porous compartmental plates; radii solid; alae not cleft; basis calcareous, tubiferous in single layer. This new species belongs to the genus Fistulobalanus mainly in having parietal tubes arranged in two or more rows; primary tubes with transverse septa; subsidiary tubes formed between the primary septum and outer lamina. In particular, the new species is similar to F. patelliformis in the shape of the shell, the transverse section of subsidiary tubes, the tergum and some characteristics of trophi and the cirri. However, this new species is easily distinguishable from all members of the genus Fistulobalanus in having no coloration or striations on the external surface of the shell, subsidiary tubes only appearing inside the ribbed part of the shell, and the scutum having a short adductor ridge.