Morphological and structural evolution of titanium oxide and chromium oxide films D.C. and R.F. sputtered were investigated. These materials were deposited on fused quartz and silicon wafers from pure metallic targets in mixed Ar-O-2 discharge. Transformations of the optical properties and crystallographic structures were observed for layers deposited at high temperature. The influence of D.C. or R.F. polarization on some characteristics of the coatings was also investigated. Both materials showed an amorphous structure for substrate temperatures up to 400 degrees C and a clear increase of layer density was illustrated from optical measurements. R.F. sputtering exhibited a strong effect on microstructure of the films compared to D.C. sputtering. This observation is discussed and some explanations of this phenomenon are proposed.