The critical current density of the highly oriented YBa₂Cu₃O_x bulk superconductors was measured at 77 K as a function of size and volume fraction of dispersed Y₂BaCuO₅ phase. The obtained critical current density increases with a decrease in the Y₂BaCuO₅ particle size and an increase in its volume fraction. Thisfact means that the Y₂BaCuO₅ phase contributes to increasing the pinning force. However, the dependence of the obtained values upon the morphology of the Y₂BaCuO₅ phase suggests that the pinning force by theY₂BaCuO₅ phase itself is comparable to that by other pinning sites which were inevitably formed during processing. The critical current density under the flux creep was tried for estimation using the virtual critical current density in the flux creep-free case calculated from a linear summation and analytical data of morphology of the Y₂BaCuO₅ phase.