The change of superconductive property by electron irradiation was studied in YBa 2Cu 3O x, x=6.9, 6.6 and 6.4. By the irradiation the transition temperatures measured by electrical resistivity shift from 87 to 83 K, 58 to 36 K, and 22 to below 10 K for x=6.9, 6.6 and 6.4, respectively. The critical current densities increase in x=6.9 after irradiation, but a slight decrease is found in both x=6.6 and 6.4. Time-dependent magnetic relaxations are measured and activation energies for flux motion are calculated as a function of temperature. The increase of J c and activation energies for x=6.9 are attributed to the small defects produced by electron irradiation.