The hypocalcemic effects of salmon calcitonin (SCT) after oral administration in rats by means of SCT-loading double liposomes (DL) which consist of liposomes containing small liposomes were investigated. SCT-loading DL consisted of four types of the inner liposomes such as neutral liposomes (NL) and cationic charged liposomes (CL) prepared using Coatsome, and neutral (VET) and cationic charged (c-VET) liposomes prepared using a mechanochemical method and sizing to 100 nm by the extrusion procedure were prepared. DL could be prepared by a combination of mechanochemical and glass-beads methods at a high efficiency. DL produced the increase in bioavailability in all groups treated with SCT-loading liposomes except for c-VET. The bioavailability of VET-DL was not significantly different but the greatest among the samples used in this study regardless of the similar size of NL-DL and CL-DL, and was approx. 6.8-fold higher than that of SCT solution when taken orally. The group treated with c-VET showed the strongest hypocalcemic effects among the inner liposomes examined (P>0.05). Therefore, it is speculated that not only the size of liposomes but also the cationic charge plays an important role in the intestinal absorption of DL. These findings suggested the utility of DL as an oral dosage form of SCT.