Silver diffusion in superconducting YBa2Cu3O7-x (YBCO) has been studied over the temperature range 500-800 degrees C by x-ray diffraction measurements. The diffusion coefficient of Ag in YBCO was determined from the observed increase (0.12%) in the lattice parameter c as compared with the undoped sample. It was shown that the diffusion coefficient of Ag in the temperature range 500-800 degrees C changed from 1 x 10(-10) to 5 x 10(-9) cm(2) s(-1) with an activation energy of about 1.06 eV. For the Ag-doped sample, the critical transition temperature and the critical current density were increased from 90 to 92.5 K and from 60 to 98 A cm(-2) respectively in comparison with those of undoped YBCO. The possible reasons for the observed increases in T-c and J(c) due to Ag diffusion were discussed.