Magnesium oxide (MgO) thin films have been grown by unbalanced magnetron sputtering on an inclined non-aligned substrate. This technique provides a way to grow biaxially aligned MgO layers. A preferential [111] out-of-plane orientation and a strong in-plane alignment have been observed. Scanning Electron Microscopy (SEM) was used to investigate the growth mechanism of these biaxially aligned MgO layers and to examine the morphology of the layers, revealing a columnar grain structure and roof-tile surface which is limited by {001} planes. Column bundling and repeated nucleation was observed. Also, the formation of highly disrupted regions caused by local heating of the growing film has been observed. A mechanism to explain the in-plane alignment is proposed. (c) 2005 Elsevier B.V. All rights reserved.