This invention describes a novel polysaccharide prodrug of 5-fluorouracil (5-FU) with enhanced target specificity for colorectal cancer treatment, and its preparation methods. The prodrug is synthesized by chemically linking anti-cancer drug 5-fluorouracil (5-FU) with a specially selected polysaccharide with molecular weight of 10.sup.5.about.10.sup.7 Da containing galactose residues. Its distinctive characteristics are that it is a prodrug synthesized by chemically linking polysaccharides with 5-FU through different bridge links for the targeted treatment of colorectal cancer; that the polysaccharides in the chemical compound contain galactose residues; and that these polysaccharides are prepared from natural gums or plant materials. Due to these unique characteristics, as an oral preparation, the polysaccharide component of this novel prodrug can protect the active agent 5-FU from absorption (or metabolism) in the upper gastrointestinal tract and deliver a high concentration of the 5-FU to the colorectal area. Upon reaching the colorectal area, the 5-FU-galactose portion of the prodrug will bind to galectin-3, a-galactoside-binding protein implicated in tumor progression by interactions with its ligands, such as TF (Thomsen-Friedenreich, Galb3GalNAc), Tn (GalNAcaThr/Ser), and Sialy-Tn with galactose residues, which are highly expressed among colorectal cancer cells. Finally, the active 5-FU component will be released locally from the polysaccharide via enzymatic hydrolysis from the local bacterial flora, allowing it to actively kill the colorectal cancer cells. In summary, this novel target-specific prodrug can enhance the selectivity of 5-FU and increase its therapeutic effects in the treatment of colorectal cancer. In addition, with this enhanced target specificity, it is possible to maximize the 5-FU efficacy in cancer patients by having either less toxicity with the same or higher therapeutic dose, and/or administer a lower dosage (if so desired) to achieve the same therapeutic effects, but with much less toxicity. Multiple examples of various approaches to synthesize this novel prodrug are enclosed herein along with several animal model experiments to substantiate the claims as stated above.