A.C. magnetic susceptibility measurements were performed on samples belonging to the Y1-xBixBa2Cu3O7-delta superconducting system prepared by solid state-reaction route. The partial replacement of yttrium with bismuth in the not-fully oxygenated samples determines an improvement of the intergranular coupling for low levels of substitution (x less than or equal to 0.1). This behaviour is assigned to the formation of the BaBiO3-x phase at the surface of the Y-123 grains, detected from the X-ray diffraction analyses. When the substitution degree exceeds x = 0.1 the intergranular coupling becomes weaker because of the Y-123 phase fraction diminishing. The A.C. susceptibility results from samples with low substitution degree (x less than or equal to 0.05) which were further oxygenated indicates that the BaBiO3-x phase favourites the oxygen diffusion into the Y-123 grains and rises the critical temperature. On the other hand the ulterior sample oxygenation leads to a weak intergranular coupling in the superconducting samples.