The resistance transitions of Gd-diffusedpolycrystallineY123 samples have been measured as a function of temperature and magnetic field. It is deduced from experimental results that the activation energy increases when the diffusion annealing temperature increases and also the activation energy of Gd-diffused samples are larger than that undoped Y123 sample. The magnetic field dependence of U follows a power law, i.e. U a H-', with the values of a are 0.42, 0.56 and 0.61, respectively, for pure Y123, and Gd-diffused Y123 at 800 and 900 oC. The changing of Ce values from 0.42 to 0.61 imply that the thermally activated dissipative resistivity is directly associated with pinning mechanism changes from intrinsic planar defects pinning to extrinsic point defects pinning because of large Gd content into Y 123 sample by the means of diffusion annealing temperature increasing. In this paper, the possible reasons responsible for the effect of Gd-diffusion on the pinning behaviors are discussed. (c) 2007 Elsevier BX All rights reserved.