The aim of our study was to determine the impact of constant magnetic field (CMF) on the effectiveness of stabilization of the excess sludge by advanced oxidation process with Fenton’s reagent. In presented study raw excess sludge from a dairy wastewater treatment plant was used. The investigations were conducted in three different technological systems in laboratoryscale stands. In the first stage the influence of chemical reagents (Fe²⁺/H₂O₂, Fe³⁺/H₂O₂) on the parameters of sewage sludge was observed. In the second stage the importance of CMF on the final technological result in the system with static crossing on magnetic field (scCMF) and in the system with cyclical crossing on magnetic field (ccCMF) was revealed. In the third stage of the experiment the effectiveness of the system with both chemical reagents and physical elements was tested. Application of the constant magnetic field let us obtain COD reduction in supernatant and volatile solids in dry mass of sewage sludge. The importance of the physical factor was shown as low doses of chemical reagents. Similar results were achieved independently of the fact if it was tested as the improving element of advanced oxidation with scCMF or with ccCMF.