Since its discovery, insulin remains the major treatment for Type 1 diabetes and many Type 2 diabetic patients, with insulin being administered parenterally. The oral route of insulin delivery, being the most comfortable, would also be the most physiologically advantageous in taking advantage of the portal-hepatic route of absorption. However, insulin is less absorbed by the intestinal mucosa and is rapidly degraded enzymatically in the gastrointestinal tract. Polymeric biodegradable and biocompatible nanoparticles have been developed. These nanoparticles protect insulin against degradation and facilitate the uptake of insulin (associated or not associated to the nanoparticles) through a paracellular or a transcellular pathway. In this review, the physicochemical characteristics of polymer composition, in vitro release kinetics and the biological effects of insulin-loaded nanoparticles in experimental diabetes and healthy animals are discussed.