The surface geometrical and electronic structure of LiMn2O4 (001) are investigated via a density functional approach within the spin-dependent generalized gradient approximation (GGA). Large relaxations perpendicular to the (001) plane of surface and subsurface atoms are observed, which is partly responsible for the Mn dissolution problem of the material when used as cathode material for lithium ion batteries. Because of the surface effect, only Mn3+ ions are observed at the LiMn2O4 (001) surfaces, which is very active for the disproportionation reaction occurs at the electrode/electrolyte interface. The calculated results are also in good agreements with experimental observations.