Aerobic sludge digestion in presence of Fenton's reagent and hydrogen peroxide was examined. Fenton's reagent considerably improved aerobic digestion process in comparison with hydrogen peroxide as well as classical aerobic digestion. Application of Fenton's reagent also led to improvement of settling and dewatering properties of sludge and much better clarity of supernatant. Its drawback, however, is formation of chemical precipitate and apparent decrease in pH that may inhibit biochemical processes important for aerobic digestion efficiency.