The last inventory of Tunisian polychaetes diversity by Ayari et al. (2009) is updated. New records were acquired from the literature and from the current study concerning species collected in the tidal channels of the Gulf of Gabès (2016-2017) and the re-examination of some species deposited in the collection of the Tunisian National Institute of Marine Sciences and Technologies. This inventory, reviewing the taxonomy, nomenclature, and biogeographic distribution of the Tunisian polychaetes, includes 390 species belonging to 52 families, among which the Serpulidae (41 species) and Syllidae (36 species) are the most diverse. In total, 37 species previously reported are currently removed from the Tunisian polychaetes list. An additional 121 new species are added, including 23 species collected in the tidal channels and 6 species in the reference collection previously misidentified as their congeners. Morphological differences between the latter are briefly discussed and figured. Among these species, Laonice bahusiensis, Laonice norgensis, and Scolelepis neglecta are extending their Mediterranean distribution, while Sternaspis thalassemoides and Caulleriella mediterranea are probably reported for the first time after their original description. In addition, this current inventory allows us to discuss the establishment status of 17 Non-Indigenous polychaete species (14 established, 1 casual, and 2 cryptogenic) found in Tunisian waters.