Electronic structures of halogen bridged mixed-valence (MV) complexes Cs2Au2X6 (X=I, Br, and Cl)have been investigated by means of reflectivity measurements. We have observed five polarization-dependent opti-cal transitions in the energy range of 0.6-5.5eV. The lower-lying three bands below～3eV are due to the intermolecular transitions from AuX2 to Aux4 molecules, while the others are assigned to the intramolecular transitions. The optical ap Egap increases from 1.31 eV for X=I to 2.04 eV for X=Cl, due to enhancement of the nearest-neighboring Coulomb repulsion V and the Jahn-Teller distortion of AuX4 (S). We further investi-gated extemal pressure effects on the electronic state, and found pressure-induced disappearance of the Raman-active Au-Br stretching modes, which indicates an electronic phase transition from the MV state to a single-valence (SV) state.