We present the electronic, magnetic, and structural properties of the cubic perovskite oxide BaMnO3 in both bulk and surface geometry. BaMnO3 is reported as keeping the cubic phase even at low temperatures. The calculations are based on the density functional theory (DFT) within plane-wave pseudopotential method and spin-polarized Generalized Gradient Approximation (GGA) of the exchange-correlation functional. The systems studied are treated in ferromagnetic order. The structures of electronic bands and density of states of the systems show half-metallic behavior in both bulk and BaO- and MnO2-terminated (001) surfaces of E2(1) structure. The calculated magnetic moment of bulk structure is 3.00 mu(B), which is largely conserved at surface geometries. Average surface and relaxation energies are also calculated. The rumpling of atoms in relaxed surfaces is determined. It is seen that the relaxation of oxygen relative to metal ion is always in outward direction for both terminations indicating a positive rumpling. (C) 2010 Elsevier B.V. All rights reserved.