The effect of Yb diffusion on structural evolution and superconducting properties of YBa2Cu3O7-x (Y123) prepared in the bulk polycrystalline form were studied. The ytterbium (Yb) diffusion in superconducting Y123 ceramic has been studied over the temperature range 800-900 degrees C by energy dispersive X-ray fluorescence technique (EDXRF). The temperature dependences of the Yb diffusion coefficient in grain (D-1) and over the grain boundaries (D-2) are described by the relations: D-1 = 4.8 x 10(-6) exp(-1.15/kT) and D-2 = 2.2 x 10(-5) exp(-1.05/kT). For the Yb-doped sample, critical current density was increased from 1.64 x 10(4) to 1.91 x 10(4) A/cm(2) at 5 K and 56 to 135 A/cm(2) at 77 K in comparison with those of undoped Y123 sample. In addition, the critical transition temperature increases by about 3 K compared with the pure Y123. It is found that J(c) can be improved by the diffusion doping of Yb in Y123, which may be due to improving the structural quality at the grain boundaries and stress-field pinning effect. (C) 2007 Elsevier B.V. All rights reserved.