Abstract . – A new species of Janiroidean isopod, Austrofilius majoricensis sp. nov., from Majorca (Balearic Islands, Western Mediterranean), is described. This is the second record of the genus in the Northern Hemisphere. It is mainly distinguished from A. mediterraneus, the other Mediterranean species of the genus, by the female operculum, which displays 9-10 distolateral setae at each side compared with only four distolateral setae in A. mediterraneus. Furthermore, the palp segment 2 of the maxilliped has the distomedial margin serrated (with three teeth), and the proximal segment of antenna 1 does not display spines on the distal margin. In addition, the rostrum of Austrofilius majoricensis sp. nov. has a slightly concave distal margin and smooth distolateral margins, whereas the lateral margins of the head are also smooth. The presence of Austrofilius in the Mediterranean is discussed.