The columnar structure in obliquely evaporated silicon oxide layers was investigated by transmission electron microscope (TEM). For TEM studies of these layers, samples were made by low angle ion-beam thinning of cross-sections, the planes of which were determined by the normal of the film and the direction of evaporation. Increasing the angle of evaporation from 5° to 30° (measured from the plane of the substrate), a change from a well–defined columnar structure to a striated structure was observed, for layers evaporated both under “low-rate” and “high-rate” conditions. There is a clear-cut dependence of the orientation of columns (αc) upon the angle of evaporation (α), however deviating from the “tangent rule” (tanαc=2tanα).