Deficiency in alpha-Klotho is involved in the pathogenesis of vascular calcification. Since intermedin (IMD)(1-53) (a calcitonin/calcitonin gene-related peptide) protects against vascular calcification, we studied whether IMD1-53 inhibits vascular calcification by upregulating alpha-Klotho. A rat model of chronic kidney disease (CKD) with vascular calcification induced by the 5/6 nephrectomy plus vitamin D-3 was used for study. The aortas of rats with CKD showed reduced IMD content but an increase of its receptor, calcitonin receptor-like receptor, and its receptor modifier, receptor activity-modifying protein 3. IMD1-53 treatment reduced vascular calcification. The expression of alpha-Klotho was greatly decreased in the aortas of rats with CKD but increased in the aortas of IMD1-53-treated rats with CKD. In vitro, IMD1-53 increased alpha-Klotho protein level in calcified vascular smooth muscle cells. alpha-Klotho knockdown blocked the inhibitory effect of IMD1-53 on vascular smooth muscle cell calcification and their transformation into osteoblast-like cells. The effect of IMD1-53 to upregulate alpha-Klotho and inhibit vascular smooth muscle cell calcification was abolished by knockdown of its receptor or its modifier protein, or treatment with the protein kinase A inhibitor H89. Thus, IMD1-53 may attenuate vascular calcification by upregulating alpha-Klotho via the calcitonin receptor/modifying protein complex and protein kinase A signaling.