The decomposition behaviour in supersaturated Al + (1-6.4) at% Zn has been investigated using electrical resistivity and microhardness measurements in the temperature range from room temperature to ~500° C. The experimental results showed that (i) both the temperature coefficient of resistivity and the relaxation time of the free electrons diminish as the concentration of Zn increases in the alloy; (ii) the early stage decomposition of the supersaturated alloys via Guinier-Preston zone formation is accompanied by an appreciable increase in the microhardness of about 80 MPa per 1 at % Zn; (iii) the obtained activation energy of 0.41 eV for the precipitation process of the dissolved zinc atoms is close to the migration energy of zinc in aluminium which indicates that the precipitation mechanism is characterized by the migration and coalescence of zinc atoms.