A method for administering ECyd to a patient that realizes a continuous therapy without expressing peripheral neurotoxicity caused by ECyd and that exhibits an excellent therapeutic effect and prolongs patient survival. An antitumor agent containing ECyd or a salt thereof and a method of administering it to a cancer patient through continuous intravenous administration at a dose of 1.30 to 8.56 mg/m2 in terms of ECyd, for each administration period of 2 to 336 hours.
