A polymer incarcerated ruthenium (PI Ru) catalyst for the oxidation of alcohols with molecular oxygen has been developed. The catalyst was prepared from a polystyrene-based copolymer with ruthenium chloride hydrate as the metal source. The choice of ruthenium species was important to obtain high catalytic activity as well as for the suppression of leaching of ruthenium. In the presence of 5 mol % of PI Ru and 15 mol % of 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO), alcohols were oxidized using molecular oxygen at atmospheric pressure to afford the corresponding aldehydes or ketones in good to excellent yields. The catalyst could be recovered and reused at least ten times without loss of activity.