Dielectric, anti-reflective or high reflective systems consist of low and high refractive index layers. Common systems are oxides. The preparation of low refractive index MgF2-films of optical quality by means of an anhydrous low temperature sol-gel synthesis is presented. The MgF2-sol is prepared by spin-coating on silicon and glass substrates. Various film thicknesses between 20 nm and 435 nm have been deposited. It has been shown that the thickness increase is proportional to the number of coating steps. The deposited MgF2-filMS consist of 10 nm to 20 nm large nanoparticles and have smooth surfaces with an average roughness (R-a) of (1.7 +/- 0.3) m. The optical constants n and k of the films are in agreement with the literature data of bulk-MgF2. (C) 2007 Elsevier B.V. All rights reserved.