An oil-resistant agent for paper, which contains a non-fluorine copolymer that has a repeating unit formed from (a) an acrylic monomer having a long-chain hydrocarbon group with 7-40 carbon atoms and a repeating unit formed from (b) an acrylic monomer having a hydrophilic group. The oil-resistant agent for paper also contains a liquid medium that is composed of water and/or an organic solvent, preferably of water or a mixture (aqueous medium) of water and an organic solvent. The non-fluorine copolymer preferably has a repeating unit formed from (c) a monomer having an ion donor group in addition to the repeating units formed from the monomers (a) and (b). Also disclosed is an oil-resistant paper having an oil-resistant layer including the oil-resistant agent for paper, and starch or modified starch, on a surface of the paper as well as a method of treating paper.