Abstract The whole Aegean Sea hosts 27 alien decapod crustaceans (21 Indo-Pacific, 6 Atlantic species). Ten of these species (3 Dendrobranchyata, 1 Caridea, 6 Brachyura) were only reported along the Greek coasts of the Aegean Sea. Among them, six species were originated from the Indo-Pacific areas and four species from the Atlantic coasts. On the other hand, 6 of the 27 alien decapods were collected only on the Turkish Aegean coasts (5 Indo-Pacific species, 1 Atlantic species). The possible causes for this differentiation could be attributed to several factors.