The hyperfine interactions at Ru-99(<--Rh-99) dispersed in YBa2Cu3O6.8 and YBa2Cu3O6 were studied by means of time-differential perturbed-angular-correlation (TDPAC) and emission Mossbauer spectroscopy. The TDPAC and Mossbauer measurements show that Ru ions are in the tetravalent state and exclusively occupy the Cu-1 sites, which form one-dimensional Cu-O chains in the orthorhombic phase. The oxygen coordinations around the Ru ions are discussed on the basis of the observed electric field gradients at Ru-99 in YBa2Cu3O6.8 and YBa2Cu3O6.