The effects of copper(II) sulfide (CuS) additions on the structure, electrical properties and AC susceptibility of YBa 2 Cu 3 O 7 (CuS) x superconductors for x = 0 to 5.0 wt. % were investigated. The solid state reaction method was used to prepare the samples. The non-added sample showed the highest onset temperature T c-onset (93 K) and zero-resistance temperature T c-zero (90 K). Addition of CuS lowered both T c-onset and T c-zero, and broadened the transition width. A double transition was observed in x ≥ 2.0 wt. % samples. This showed that CuS weakened the coupling between grains and suppressed the superconducting percolation leading to a double transition. The room temperature resistivity increased from 1.51 mΩ cm for x = 0 to 17.7 mΩ cm for x = 5.0 wt. %. The peak of the imaginary part of the susceptibility (χ"), T p shifted to lower temperatures with addition of CuS. The x = 1.0 wt. % sample showed the highest critical current density, J c (T p = 69.5 K) of 24.1 A cm −2 .