We have developed new substituted langasite crystals in order to increase piezoelectric constants. By solid state reaction and micro-pulling down technique, La_<2.75>Sr_<0.25>Ta_<0.625>Ga_<5.375>O_<14> and Sr_3TaGa_3Si_2O_<14> were obtained as single phase with langasite-type structure. These crystals with bulk size were also grown by the Czochralski technique.
