The valence band electronic structure of a BaTiO₃-derived oxide quasicrystal (OQC) is studied by photoemission using momentum microscopy. An upward-dispersive Q_2p band is identified, and it can be assigned to a combination of in-plane orbitals according to the symmetry and the overlap of the wave functions. In addition, the signature of Ti_3d states near the Fermi level is observed, which results in a metallic character of the OQC with 3d¹ occupation. Our experiments reveal two-dimensional electronic states within the OQC based on a symmetry-adapted decomposition of photoelectron intensity distribution in the momentum space.