We evaluated cytotoxic effect based on the MTT assay and identified altered proteins in 5-FU(fluorouracil) treated HT29 cells using two-dimensional gel electrophoresis and MALDI-TOF/TOF-MS. As proteins inducing apoptosis, siah binding protein 1 and p47 protein isoform a were up-regulated and tumor protein translationally-controlled 1 was down-regulated by 5-FU treatment. And mannose 6 phosphate receptor binding protein 1 controls DNA mismatch repair system was increased. We suggest 5-FU promotes a cytotoxicity under the action of these proteins in colon cancer cells.