Provided is a catalyst for a Fenton system, and a method of preparing the same. The catalyst includes one or more species of d0-orbital-based or non-d0-orbital-based catalyst including NO3−/SO42−/H2PO4−/HPO42−/PO43− functional groups on the surface thereof. The method includes preparing a d0-orbital-based or non-d0-orbital-based transition metal oxide; and preparing a transition metal oxide catalyst comprising a NO3−, SO42−, H2PO4−, HPO42−, or PO43− functional group on the surface of the catalyst via nitrification, sulfation, or phosphorylation of the transition metal oxide.