A new superconductor Tl 2 Ba 2 Ca 3 Cu 4 O 12 has been synthesized with a T c onset at 120 K and a zero resistance at 104 K. The X-ray powder investigation and HREM study allow a structural model to be proposed. The tetragonal cell, with a=3.852 Å and c=42.00 Å, corresponds to the intergrowth of triple rocksalt type layers with quadruple oxygen deficient perovskite layers leading to the structural formulation [ (TlO) 2 (BaO) ][ BaCa 3 Cu 4 O 9]. This oxide which represents the member n=3, m=4 of the series (A O )n (A′ CuO 3−y)m, shows that T c seems to tend towards a limit as the number of copper planes forming the perovskite layers increases.