The method of ultrasoft pseudopotential within the generalized gradient approximation has been employed to study the elastic constants and electronic structure of (Al,Si)3Sc precipitate with L12 structure in Al-base alloys. Based on the calculated results, the elastic properties of (Al,Si)3Sc precipitate were investigated. The Young’s and shear modulus of the polycrystals for (Al,Si)3Sc precipitate were calculated using Voigt-Reuss-Hill averaging scheme. The calculated results of elastic properties showed that the (Al,Si)3Sc precipitate has a strengthening effect in the Al matrix, owing to the larger shear modulus differences between (Al,Si)3Sc and Al matrix. The calculated results also showed that (Al,Si)3Sc precipitate is brittle in nature.