To provide a marker for determining sensitivity of a patient to an anti-cancer agent, which marker can determine whether or not the patient has a therapeutic response to the anti-cancer agent, and novel cancer therapeutic means employing the marker. The marker for determining the sensitivity of a subject to an anti-cancer agent including oxaliplatin or a salt thereof, fluorouracil or a salt thereof, and levofolinate or a salt thereof, the marker containing one or more genes selected from the group consisting of ALAD gene, C20orf43 gene, CABLES1 gene, CDC14B gene, GDA gene, HOXB6 gene, RPL7AP27 gene, TMEM18 gene, and UGT2B10 gene.