The invention relates to an enteric-coated capsule containing cationic nanoparticles for oral insulin delivery, in particular to a type of cationic nanoparticle including a polycationic and mucoadhesive polymer and a biodegradable polymer, wherein each of the nanoparticles has positive surface charge and enhanced permeability for paracellular insulin delivery; the enteric-coated capsule further includes a pH-sensitive polymer as the coating. The enteric-coated capsule containing cationic nanoparticles, when being orally administered to a subject, are configured to prevent the acidic degradation of the active substance such as insulin before being released from said cationic nanoparticles to a specific absorption site along the gastrointestinal tract.