In this work, we report our study of the microstructure and mechanical properties of pure Ti, Ti-11Al, Ti-47Al and Ti-6Al-4V nanostructure coatings on AZ91D Mg alloys prepared using DC magnetron sputtering. The fine structures of the coating (see fig. 1 for Ti-6Al-4V coating) are presented. The hardness of the coatings were tested on a CSEM nano-hardness tester with a Berkovich diamond intender. Hardness values were obtained from analyses using the Oliver-Pharr scheme. The hardness of the nanostructure coating increases from about 3.5GPa up to about 6.8GPa when the aluminium concentration increases from zero to 47at.%. Maximum hardness value was found on the Ti-6Al-4V coating, about 7.3GPa. The elastic modulus of the pure Ti coating has the lowest modulus and strain burst “pop-in” has been observed on Ti-47Al coating.