MgO substituted polycrystalline BaTi2O5 (BT2), Ba1-xMgxTi2O5 (BMT2), was prepared by a floating zone method (FZ-melting). The dielectric property of BMT2 was investigated bySubscript text an AC impedance method. At x = 0.005 MgO, the permittivity (r) showed the maximum value of 5800 for FZ-melted specimens. The Curie temperature (Tc) decreased with increasing x and the permittivity showed a flat peak at x ≥ 0.03. Second phases of BaTiO3, Ba6Ti17O40 and Ba4MgTi11O27 were identified in polycrystalline BMT2. BaTiO3 and Ba6Ti17O40 could be due to the decomposition of BT2 at high temperatures.