In sintering and annealing of ceramic superconductors, diffusion of oxygen and sample weight changes are two important parameters to understand. In this work, we have undertaken to make weight loss measurements at different temperatures. At 400–600 °C, the weight loss data can be simply interpreted via one diffusion process. The Arrhenius activation energy is found to be ca. 23 kcal/mole. At 500 °C, the isotropic diffusion constant was found to be 9.5 × 10−12 cm2/s. Above 600 °C, the weight loss curves become complex and indicate the occurrence of two diffusion processes. The oxygen loss and the oxygen uptake data are interpreted via our present knowledge of this system.