The effect of Mg content on some of the electrical parameters and the microhardness of Al-Mg alloys has been investigated. Namely, the dependence of the temperature coefficient of resistivity, a all, the electronic relaxation time, t all, and the electron-impurity scattering power, D h , on the Mg content in the alloys has been studied. On the other hand, the influence of dissolved Mg on the microhardness ofAl- Mg alloys has been evaluated. In addition, the decomposition behaviour of the supersaturated Al-Mg alloys has been followed and characterized.