Extra-cellular product anti-biofouling against marine invertebrates which are common to the biofouling, which contains an extract of the supernatant of an Alteromonas sp. Culture. Anti-biofouling composition, comprising said extra-cellular product and a biopolymer. The use of said extra-cellular product for preparing a composition useful for inhibiting the marine micro- and macro-biofouling, and the process for preparing said extra-cellular product.