We have used an initio self-consistent field (SCF) molecular orbital approach to investigate the equilibrium geometry and relative stability of the C4O4^m^-(m=0, 1, 2, 3, 4). We find that the series of anions studied go through the change from non-aromatic structure to aromatic structure and then to anti-aromatic structure again with the relative stability order: C4O4^-^.>C4O4^2^->C4O4>C4O4^3^-^. >C4O4^4^-.

Key words: AB INITIO CALCULATION, STABILITY, AROMATIC COMPOUNDS, STRUCTURAL CHEMISTRY