The electrical resistivity was measured on Al-Li and Al-Sc systems annealed and aged at various temperatures to determine the equilibrium solubility of Li and Sc in aluminium. The residual resistivity for Li and Sc in aluminium was determined to be 0.79μΩ㎝/at% in Al-Li system and 3.8μΩ㎝/at% in Al-Sc system, respectively. These values are influenced to the determination of the solute concentration in matrix. The Li and Sc concentration in matrix due to coarsening of the precipitates linearly increases with t^(-⅓). The Li and Sc concentration in equilibrium with the precipitates of infinite size, i. e, the equilibrium solubility of Li and Sc in aluminium is given by applying Ostwald ripening theory developed by Adrell. The values of the equilibrium solubility of Li and Sc in aluminium were determined to be 4.60 at% at 493K ; 4.93 at% at 513K in AI-Li system and 0.008 at% at 673K ; 0.013at% at 703K ; 0.019 at% at 733K in Al-Sc system, respectively.