Today investigators take intense interest in gallium nitride nanofilms as to a perspective material for semi-conductor nanoelectronics. At 300 K its band-gap width is equal to 3,39 eV. It is a wide band gap III-V semiconductor. GaN bulk crystal is a strong chemical compound, as experimental values of atomization energy and bond length are equal, accordingly, 2,20 eV/at and 0,17 nm. Thin films on its basis are applied to creation of light-emitting diodes and the lasers radiating in dark blue area of a spectrum, for manufacturing of the electronic devices working at high frequencies, temperatures and in excited environments. Gallium nitride thin films crystallize in stable hexagonal (wurtzite) or meta-stable cubic (blende) crystal structures. It depends on substrate type, on which there is a growth of gallium nitride films. But the nature of their stability in diamond like lattices is not quite clear till now, as atoms of nitrogen and gallium have the big distinction in atomic radiuses and electronegatives.The purpose of presented work is investigation of gallium nitride nanofilm’s stability. Using a wurtzite crystal lattice data initial GaN nanofilms with various number (from 160 up to 1200) atoms was constructed. After that variation procedure of energy minimization was used by nonlocal density functional method. The nanostructure optimization by algorithmic steepest descent method along the binding potential energy surface in a configuration space of nanosystem was performed. The main results were as following. 1. At small number of atoms values of nanofilm’s atomization energy (1.82 eV/at) is essential below crystal one. 2. Value of nanofilm’s atomization energy is increased with increasing of number of atoms, passing through a local maximum (2.14 eV/at) at 1000 atoms.3. Energy of lattice optimization counting per atom has also a maximum (0.037 eV/at) at 1000 atoms. 4. Equilibrium bond lengths (~0.20 nm) in all synthesized nanofilms are greater than bulk one.