In this study, a titanium surface was chemically modified with calcium ions and assessed for its influence on osteogenic differentiation and molecular responses of human mesenchymal stem cells (hMSCs). Titanium disks were treated with NaOH (NaOH treatment), NaOH + CaCl2 (CaCl2 treatment), or NaOH + Ca(OH)2 (Ca(OH)2 treatment). Ca(OH)2 treatment caused significantly greater calcium incorporation onto the titanium surface and apatite formation than CaCl2 treatment. The morphology of hMSCs differed on CaCl2- and Ca(OH)2-treated disks. The osteopontin (OPN) expression in hMSCs cultured on CaCl2-treated titanium was significantly higher than that in cells cultured on NaOH-treated disks; OPN expression was significantly higher in cells cultured on Ca(OH)2-treated disks than on un-, NaOH-, and CaCl2-treated disks. Osteocalcin (OCN) protein expression in hMSCs cultured on Ca(OH)2-treated disks was significantly higher than that on all the other disks. Comparative expression profiling by DNA microarray and pathway analyses revealed that calcium modification of the titanium surface induced integrin β3 after OPN upregulation and promoted Wnt/β-catenin signaling in hMSCs. In addition, Ca(OH)2 treatment upregulated the expression of bone morphogenetic protein 2, cyclooxygenase 2, and parathyroid hormone-like hormone in comparison to CaCl2 treatment. These observations suggest that calcium-modified titanium surfaces affect osteogenic differentiation in hMSCs and that Ca(OH)2 treatment induced osteogenic differentiation in hMSCs, whereas CaCl2 treatment had a limited effect. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 101A: 2573–2585, 2013. © 147.