Al-substituted langasite (La3Ga5-xAlxSiO14) single crystals up to x = 0.9 have been grown by the Czochralski method. The effective segregation coefficient (k(eff)) of Al in langasite was estimated to be between 1.03 and 1.07. X-ray structural analysis indicated that Al occupied the octahedral and the two kinds of tetrahedral sites in the crystal lattice. The piezoelectricity of Al-substituted langasite was also compared with that of langasite. By Al substitution, while the piezoelectric constant \d(11)\ became slightly larger, d(14) was smaller. The electromechanical coupling factors (k(12), k(25) and k(26)) became larger. It was found that Al substitution of langasite created a material with preferred electromechanical properties applicable to the next generation of advanced digital communication systems.