The piezoelectric properties of some perovskite ferroelectric materials have been investigated. The Curie temperature of $Nb^{+5}$ deped $BaTiO_3$ is lowered, and that of $La^{+3}$ doped BaTiO3 varies depending on whether the ionic neautrality of the ceramics is satisfied. The optimum sintered density of BaTiO3 system is obtained when the specimen is sintered for about an hour at 1300-140$0^{circ}C$ (the optimal sintering temperature of PZT is also about 130$0^{circ}C$). The electromechanical coupling factor of PZT is reported to be larger than that of $BaTiO_3$ system.