We prepared a new two-dimensional oxyantimonide, BaTi2Sb2O, which shows a superconducting transition at 1.2 K, representing the first superconductivity in a system with Ti3+ (d1) in a square lattice. The TiO2Sb4 mixed anionic coordination stabilizes a unique half-filled Ti dxy orbital configuration in Ti2O plane, which is analogous to Cu2+ (d9) in the high-Tc superconductors. A charge density wave (CDW)- or spin density wave (SDW)-like anomaly appears at 50 K, which is significantly reduced compared with 200 K for the isostructural and non-superconducting BaTi2As2O.