TSMTG (top seeding melt texture growth)-processed YBa 2 Cu 3 O 7−δ ceramics have reached such critical current densities (J c ) that it is now possible to envisage technical applications such as magnetic bearings or fault current limiters. Most authors believe that in this material, defects (such as Y-211 inclusions, oxygen vacancies, dislocations, stacking faults, etc) can act as pinning centres and hence increase critical current densities. The effects on the critical current density of a uniaxial pressure, applied along a direction perpendicular to the c-axis of Y-123, at 400 • C under an air atmosphere are investigated. These conditions were chosen to avoid oxygen loss in the samples, because oxygen content is the most critical parameter for superconducting properties. Thus this allows a sample with the same oxygen content to be compared directly before and after experiment. TSMTG-processed Y-123 ceramics exposed to thermomechanical treatment show a complex behaviour. For low pressures (lower than 2 MPa) a significant increase in the critical current density (up to 1.37 times at H = 0, for a pressure of 1.38 MPa applied for 22 h at 400 • C under an air atmosphere) is observed and attributed to an increase in the dislocation density. For higher pressures, the critical current densities under low magnetic fields are always lower but sometimes slightly higher at moderate magnetic fields (between 1-3 T).