The first successful elaboration of a new class of thermodynamically stable nano composite materials is reported. These were obtained in three steps: 1) mixing of solutions of large diblock copolymers and of modified mineral nanoparticles; 2) spincoating the composite solution on a solid substrate; 3) annealing the resulting film till quasi-equilibrium self organization is reached. A composite organic-inorganic material is obtained, with a periodic distribution of the particles in the polymeric matrix