Polysaccharides are abundant in nature, renewable, nontoxic, and intrinsically biodegradable. They possess a high level of functional groups including hydroxyl, amino, and carboxylic acid groups. These functional groups can be utilized for further modification of polysaccharides with small molecules, polymers, and crosslinkers; the modified polysaccharides have been used as effective building blocks in fabricating novel biomaterials for various biomedical applications such as drug delivery carriers, cell-encapsulating biomaterials, and tissue engineering scaffolds. This review describes recent strategies to modify polysaccharides for the development of polysaccharide-based biomaterials; typically self-assembled micelles, crosslinked microgels/nanogels, three-dimensional hydrogels, and fibrous meshes. In addition, the outlook is briefly discussed on the important aspects for the current and future development of polysaccharide-based biomaterials, particularly tumor-targeting intracellular drug delivery nanocarriers.