Provided is a novel marker for determining sensitivity to an anti-cancer agent. The marker for determining sensitivity to an anti-cancer agent, the anti-cancer agent including oxaliplatin or a salt thereof, fluorouracil or a salt thereof, and levofolinate or a salt thereof, the marker comprising one or more substances selected from the group consisting of 2DG6P, 2MSE, CSSG, DOPM, GSSG, I4A, P2CB, 1-methyl-2-pyrrolidone, ASP, benzamide, glucaric acid, GL6P, Gly-Gly, HYPT and HYPX.