Assemblable ventilation grille formed by modular elements provided, on the sides to be joined together, with complementary male and female joints or fastening elements so that they may be combined to form grilles of variable size suited to the varying requirements of the market. The said male and female fastening elements have a thickness smaller than that of the grille modules and are situated at the ends of the sides to be joined together, along the frame sides and if necessary also in intermediate zones of the said sides to be joined together, underneath the fins, all of which so as not to be visible from the front side of the grille obtained by means of the combination of these modules.