Self diffusion coefficients of oxygen in PLZT ceramics were evaluated to estimate the vacancy structure by the oxygen-18 isotope exchange reaction and the isotope analysis by the secondary ion mass spectroscopy (SIMS). In the piezoelectric composition of PLZT (10/50/50), the oxygen vacancy concentration was estimated as about one ppm/mol by means of oxygen diffusion measurements and it did not change by doping impurities except for manganese. It was considered that point defects existed at all sites of the perovskite structure of PLZT. On the other hand, the oxygen vacancy concentration increased to 100ppm/mol for manganese doped samples, and the reason was considered that manganese ions were reduced during sintering and that the oxygen vacancies were created to compensate the charge imbalance. In the transparent PLZT (9/65/35), the oxygen vacancy was ten times as much as that in PLZT (10/50/50). The increase in oxygen vacancy was ascribed to volatilization of lead or variation of solubility of lanthanum in B site. All samples showed extraordinary oxygen diffusion at high temperatures near the surface, which was ascribed to the volatilization of PbO.