Nanoidentation responses of Al(2)O(3) coatings obtained using chemical vapour deposition on cemented carbides were studied and related to the Al(2)O(3) modification and microstructure. Five different Al(2)O(3) layers were studied: (i) kappa-Al(2)O(3), (ii) alpha-Al(2)O(3), obtained through the kappa -> alpha phase transformation, (iii) as-grown alpha-Al(2)O(3) with (1012) texture, (iv) as-grown alpha-Al(2)O(3) with (1014) texture and (v) as-grown alpha-Al(2)O(3) with (0001) texture. All the Al(2)O(3) coatings were deposited to a thickness of at least 6 mu m onto identical WC - 6 wt.% Co cemented carbide substrates. Nanoindentation was performed on taper-section specimens. The microstructure, phase and texture were elucidated by using transmission electron microscopy, scanning electron microscopy and X-ray diffraction. Nanoindentation responses of the as-grown, textured alpha-Al(2)O(3) coatings were compared with kappa-Al(2)O(3) and alpha-Al(2)O(3) formed as a result of the kappa -> alpha phase transformation. The as-grown, textured alpha-Al(2)O(3) layers exhibited clearly a higher hardness and Young's modulus than the alpha-Al(2)O(3) and the alpha-Al(2)O(3) layers formed as a result of the phase transformation. Only slight differences in hardness and modulus could be detected between the (1012), (1014) and (0001) textured alpha-Al(2)O(3) films. Among these the (1012) textured alpha-Al(2)O(3) coating exhibited the lowest hardness and modulus. Opposite to earlier reports, the present investigation clearly showed that kappa-Al(2)O(3) exhibited both the lowest hardness and Young's modulus as compared with the other studied coatings. It is emphasised that the earlier nanoindentation investigations that were intended to deal with alpha-Al(2)O(3) were in fact performed on transformed kappa-Al(2)O(3). (c) 2007 Elsevier B.V. All rights reserved.