Magnetic relaxation data have been taken on zone‐melted and sintered YBa2Cu3Oxsamples over wide temperature and magnetic field ranges. We have found that magnetic relaxation varies greatly in the samples with different microstructures and crystallographic orientations. Flux‐creep rates have been found to be reduced in the zone‐melted samples owing to large amounts of intragranular crystal defects such as edge dislocations and stacking faults. An important flux‐pinning behavior related to the pinning potential distributions has been observed in the samples. The relationship between microstructural orientation and pinning potential distributions in YBa2Cu3Oxis discussed.