Supersaturated Al-10 and 15 mol% Li solid solutions were prepared by means of heat treatments under high pressure and high temperature, and the variations of elastic modulus, electrical resistivity and micro-Vicker’s hardness in these solid solutions during isochronal ageing up to 673 K were investigated. The maximum shear modulus was observed during the precipitation of the delta’ phase at 453 K ageing, The difference in the decomposition behaviour of several specimens obtained by high-pressure solid solutioning and the conventional one is discussed based on the results of elastic moduli measurements.