All-trans Retinoic Acid (atRA), is known as a member of retinoid, and the atRA nano-particle with coated by CaCO3 (nanoegg -atRA), was recently developed as a new drug delivery system (DDS). This nanoparticles stimulated insulin secretion from islets in a glucose-dependent manner at streptozotocin (STZ)-induced diabetes. The stains on pancreas of Wistar rat at STZ induced diabetes, which was subcutaneous administered nanoegg -atRA 6 mg/head/week for 141 days, showed not only the expression of PDX-1 but also the presence of beta cell in islet of Langerhans. Furthermore, the increase of insulin concentration in plasma was also observed. Our data indicate that nanoegg -atRA might contribute to the regeneration of beta cells in vivo, and provide useful information for future therapy of diabetes mellitus.