The aim of the study was to develop and characterize polymeric nanoparticles as a sustained release system for salmon calcitonin (sCT). Nanoparticles were prepared by a double emulsion solvent evaporation method using Eudragit RS and two types of a biodegradable poly(lactic-co-glycolic) copolymer (PLGA). It was demonstrated that sCT was incorporated into nanoparticles with encapsulation efficiencies in the range 69-83%. In vitro release studies, unconventionally conducted in 5% acetic acid, showed great differences in sCT release time profiles. Nanoparticles with fast release profile (Eudragit RS, PLGA/Eudragit RS) released 80-100% of the encapsulated drug within a few hours. In contrast, the sCT release from pure PLGA nanoparticles was very slow, incomplete and reached only 20% after 4 weeks. In vivo study, conducted in Wistar rats, proved that elevated serum sCT levels could be sustained for 3 days after subcutaneous administration of PLGA nanoparticles and the achieved bioavailability was increased compared to sCT solution.