The structure of the O-4(2+) dication has been studied theoretically using a few conventional theoretical methods. We found the O-4(2+) dication to be a metastable species with a perfect square structure. The molecular orbital analysis reveals that this dication is the first all-oxygen aromatic system with 6pi electrons. Although the O-4(2+) dication is highly thermodynamically unstable, we believe that appropriate counteranions with very high electron detachment energy (superhalogens) can be found to form a solid-state compound containing O-4(2+). Another way to probe the planar aromatic tetra oxygen dication could be a double-photoionization process of the (O-2)(2) dimer.