Ecsenius caeruliventris, known commonly as the Bluebelly blenny in Indonesia, is a species of combtooth blenny in the genus Ecsenius. It is a tropical blenny found in the western Pacific ocean, specifically in Sulawesi, Indonesia. Male Ecsenius caeruliventris can reach a maximum length of 2.4 centimetres, while females can reach a maximum length of 2.37 centimetres; it is one of the smallest blennies in Ecsenius. The species name means "Sky-blue belly" from the Latin words caeruleus and ventris, referring to the blue abdomen on the species; the common name is derived from this. The species is most similar to its sister taxon E. shirleyae and E. bandanus.