1. The addition of zirconium to alloy 01420 leads to metastable zirconium phase and formation of dispersed equilibrium phases S (and possibly γ) characteristic of Al-Mg-Li alloys. Along with zirconium contained in the solid solution, these phases evidently inhibit recrystallization. 2. Models were plotted of the changes in the mechanical properties and the aging effect of Al-Mg-Li-Zr alloys in relation to the magnesium and lithium concentrations. 3. The larger aging effect with increasing lithium concentrations in the Al-Mg-Li-Zr alloys investigated is due to an increase in the density of δ′ precipitates (Al3Li).