The Sea Scheldt comprises the brackish (Belgian-Dutch border to Burcht) and fresh water part (Burcht to Ghent) of the macrotidal Scheldt estuary. The port of Antwerp is situated in the brackish part of the river. Brackish harbour regions are considered particularly susceptible to introductions, because the diversity of native species is usually low and the import rate of new species by ballast water is high. Canals, inland navigation and active introduction are other possible ways for colonisation. Although we have no specific research program for exotic species in the Sea Scheldt and its tidal tributaries, they are regularly encountered, e.g. during the monitoring campaigns for benthic infauna, as by-catch in the monitoring campaigns for migratory fish, on artificial substrates used for monitoring glass eel migration or on buoys. We present a non exhaustive list of 27 alien macrobenthic species (belonging to Oligochaeta, Polychaeta, Gastropoda, Crustacea and Diptera) that we encountered in the intertidal or subtidal zone since 1993. The tanaid Sinelobus stanfordi was found for the first time in Europe (Van Haaren & Soors, in prep.) The isopod Synidotea laevidorsalis is new for northwest Europe (Soors et al., submitted). Our list confirms the susceptibility of the brackish zone to alien species (19 out of 27 species), but the fresh water part also counted 13 aliens. Five species occur in both brackish and fresh water. Specific research, especially on epifauna and hard substrates, undoubtedly will reveal more alien taxa and further extend the range of the currently known taxa.