The oxidation of dissolved fluorene and 9–fluorenone was studied in dilute aqueous media using ozone–oxygen systems. The efficacy of complete degradation of the titled polynuclear aromatics (PNA) was evaluated and the products were examined. Both PNA were readily oxidized, fluorene offering less resistance to ozone oxidation than 9–fluorenone. Partially oxidized PNA (e.g. hydroxylated PNA) were formed initially and were subsequently oxidized to produce aromatic dicarboxylic acids. Oxalic acid and to a small extent, an unknown aliphatic dibasic acid were the major end–products. The destruction of these aliphatic dibasic acids required longer periods of ozonation.