Caulerpa cylindracea (Sonder) is an invasive seaweed native to south-eastern Australia. The existence of this seaweed was noticed along the coasts of 15 Mediterranean countries since 1990. Recently, many authors have revealed its negative effect on Mediterranean benthic species as well as its potential to strongly alter indigenous communities. In this study, new evidence data are given concerning the situation of this invasive taxon in Algeria and particularly about a recent spread in the western part of the Algerian coasts, near Oran.