The possibility of using a composite material (hereinafter referred to as composite) based on silica gel modified with particles of Fe(III) compounds for the highly efficient purification of contaminated transformer oils and batches of oils for long-term storage is investigated. The KSKG silica-derived composite modified with particles of Fe(III) compounds with an iron content of about 7 wt % (SiO2-7Fe-Amk-600) is found to be more effective when compared with pure KSKG silica gel for removing both acid activators for sludge formation and oil-degradation products from transformer oils. The preservation of the basic properties of oil after its purification on the SiO2-7Fe-Amk-600 composite and storage for 2 years in contact with this composite indicates the possibility of using the new SiO2-7Fe-Amk-600 composite as a stabilizer for the original and purified transformer oils.