The superconducting current density, Jc, of Y1Ba2Cu3O7−δ (YBCO) is greatly influenced by hole doping levels. Hole doping is mainly dominated by oxygen ordering, so the postannealing process is one of the essential factors for practical applications of YBCO superconductors. However, little research has been reported about the variation in Jc by annealing time. In this study, the optimal annealing conditions were studied using homogeneous c-axis oriented YBCO thin films prepared by the pulsed laser deposition method. As a result, Jc (at 77 K, 0 T) increased from 0.3 to 5.3 MA/cm2 with an annealing time in the range of 0–12 h. This result suggests that annealing for tens of hours is essential for obtaining high Jc samples, even if the film is 250 nm thick. The oxygen diffusion process was examined by applying the one-dimensional diffusion model.