Abstract: A method for producing ethylene copolymer using ethylene and at least a comonomer of unsaturated glycidyl monomer in the presence of a polymerization initiator, wherein the undesirable thermal polymerization of the unsaturated glycidyl monomer in the preparation system can be avoided and the operation can be continued for a long period of time in a stable condition. The method is characterized in that at least two kinds of polymerization inhibitors are used and the inhibition factor of one polymerization inhibitor added to the unsaturated glycidyl monomer is smaller than that of another polymerization inhibitor added to the lubricating oil for compressors and the unsaturated glycidyl monomer containing 100 to 2000 ppm of a polymerization inhibitor is introduced from the inlet side of a high pressure compressor into the reaction system and the lubricating oil containing 0.1 to 10% by weight of a polymerization inhibitor is used for the high pressure compressor.