This invention relates to a preparation process of a biaxially oriented heat-shrinkable ultra-thin film, biaxially oriented by the flat process and made of linear low-density polyethylene, characterized in that: an ethylene homopolymer or an ethylene and C.sub.4 to C.sub.18 alpha-olefinic comonomer copolymer of a density lying between 0.89 and 0.94, alone or in combination, are heated beyond the melt temperature and extruded, the extruded film is poured and cooled at the appropriate hardening temperature, the film is drawn a first time in the machine direction at the appropriate temperature between 3 and 7 times the initial dimension of the non stretched film, the film is drawn a second time in the transverse direction at the appropriate temperature between 3 and 15 times the initial dimension of the non stretched film, the biaxially oriented film is drawn a third time in the machine direction at the appropriate temperature between 1.01 and 3 times the dimension after the first draw, the biaxially oriented film obtained is cooled at room temperature. The invention also concerns an ultra-thin monolayer film obtained notably by such process. These ultra-thin films have a thickness from 6 to 11 .mu.m.