Polymer dispersed liquid crystal films were elaborated by the polymerization induced phase separation technique. In particular, the influence of the incorporation of diamond nanoparticles was investigated by measuring optical and electro-optical properties of the corresponding films. The presence of a small amount of diamond nanoparticles leads to a strong increase of the optical transmittance under an applied electrical field. This effect was attributed to a phase separation phenomenon by the formation of micron-sized aggregates of diamond nanoparticles, which was confirmed by observations carried out by optical microscopy.