The effect of calcium sensing receptor (CaSR) on tumor cell proliferation has been studied in several human cancers, and great discrepancies were found in different tumors. However, the role of CaSR in lung adenocarcinomas (LUADs) is not clear. Therefore, we investigated the function of CaSR on regulating the growth of human LUAD and its possible mechanism. The expression of CaSR protein and its relationship with pathological parameters were examined in paraffin sections from 51 LUAD patients, by immunohistochemistry. The results showed that CasR expression was negatively correlated with the Ki-67 index as well as the grade of malignancy in LUAD. Further, CaSR demonstrated anin vitroinhibitory effect on the proliferation of human LUAD A549 cells by regulating CaSR activity with agonist cinacalcet, antagonist NPS2143, or shRNA-CaSR transfection. Tumor xenograft models also verified thein vivoproliferation-inhibiting role of CaSR by subcutaneous injecting A549 cells into nude mice with or without changes of CaSR activity. Molecularly, Western blotting showed that CaSR positively regulated the activity of glycogen synthase kinase 3 beta (GSK3 beta), followed by the downregulation of Cyclin D1. We used the dominant negative mutant and the constitutively active mutant plasmid of GSK3 beta to alter GSK3 beta activity. Our functional experiments showed that the proliferation-inhibition of CaSR was suppressed by the inactivation of GSK3 beta and enhanced by the activation of GSK3 beta. These results suggested that CaSR played a proliferation-inhibiting role in LUAD, at least partially by regulating the GSK3 beta/Cyclin D1 pathway.