The crystal, electronic, and magnetic structures of the cobalt oxyselenide La2Co2O3Se2 were investigated through powder neutron diffraction measurements and band structure calculations. This oxyselenide crystallizes in a tetragonal layered structure with space group 14/mmm. The Co ion is sixfold-coordinated by two oxide ions and four selenide ions, and the face-sharing CoO2Se4 octahedra form Co2OSe2 layers. The band structure calculations revealed that the Co ion is in the divalent high-spin state. Rietveld analysis of the neutron diffraction profiles below 200 K demonstrated that the Co moments have a noncollinear antiferromagnetic structure with the propagation vector k = (1/2, 1/2, 0). The ordered magnetic moment was determined to be 3.5 mu(B) at 10 K, and the directions of the nearest-neighbor Co moments are orthogonal each other in the c plane.