Al-C at% Mg alloys (C = 0.82, 1.84, 3.76, 5.74 and 12.18) have been selected for this study. From the electrical resistivity measurements it is concluded that the resistivity increment of Al–Mg alloys (in a solid solution state) is proportional to the atomic fractional constituents (Mg and Al) as $\Delta\rho_{\rm all}=64.66\ c(1-c)~\mu\Omegarm$ cm. In addition, both the temperature coefficient of resistivity, α _all and the relaxation time of the free electrons τ _all in the alloys diminish with increasing the solute Mg concentration. The increase of the scattering power, η, with increasing C is interpreted to be due to the contribution of electron-impurity scattering. The percentage increase due to electron-impurity scattering per one atomic percent Mg has been determined as 12.99%. The Debye temperature θ decreases as the Mg concentration increases. The microhardness results showed that the solid solution hardening obeys the relation ΔHV _s = 135.5C ^0.778 MPa which is comparable to the theory of solid solution hardening for all alloys; ΔHV _s ≈ C ^0.5−0.67 MPa.