AbstractDynamic covalent bonds are established upon molecular recognition of sugar derivatives by boronic acid molecules. These reversible links can be used in a cross‐linking method to fabricate polymer‐based responsive nanosystems. Herein, the design of the first dynamic nanogels made entirely of polysaccharides (PS) is reported. Based on PS chains alternately modified with phenyl boronic acid groups and sugar moieties, these colloids self‐assemble in physiological conditions and combine the biocompatible nature of their PS backbone with the reconfiguration capacities of their cross‐linking chemistry. These dynamic nanogels are easily prepared, stable for a long time, pH responsive, and efficiently internalized by cancer cells.