Purpose: Human mesenchymal stem cells (hMSCs) are primary cells capable of differentiating to osteocytic lineage when stimulated under appropriate conditions. This study examined changes in hMSC morphology, proliferation, and gene expression after growth on machined or dual acid-etched (AE) titanium surfaces. Materials and Methods: hMSCs, isolated from adult human bone marrow, were cultured on titanium surfaces. The two specimens of titanium surfaces in this study included machined and AE titanium disks. Cell morphology was evaluated by scanning electron microscopy, and cell proliferation and collagen synthesis were estimated by measuring the amount of 3H-thymidine incorporation into DNA and 3H-proline incorporation into collagen fibers. Alkaline phosphatase (ALP) activity was determined by measuring the release of p-nitrophenol from disodium p-nitrophenyl phosphate. Changes in gene expression for bone morphogenetic protein-2 (BMP-2), Runx2 type II, Osterix (Osx), osteopontin, type I collagen, ALP, osteocalcin, and bone sialoprotein were determined by reverse-transcriptase polymerase chain reaction after 22 days of in vitro culture in osteogenic medium. Results: The two substrates had no significant effects on cell adhesion and proliferation. Morphologic characteristics were observed by scanning electron microscopy. hMSCs on the machined surface spread more and were flatter than cells cultured on the AE surface. Osteopontin mRNA expression was similar on all surfaces, and the other mRNA transcripts were increased in hMSC cultured on AE surface. In particular, BMP-2, Runx2, and Osx, three osteogenic factors that induce the progressive differentiation of multipotent mesenchymal cells into osteoblasts, were expressed more on AE titanium than on machined titanium. Collagen and ALP assays confirmed the highest level of mRNA transcripts correlated with increases in these proteins. Conclusion: These results showed that an AE titanium surface stimulated the expression of markers of osteoblastic phenotype more than a machined titanium surface. Schlagwörter: gene expression, human mesenchymal stem cells, proliferation, surface properties, titanium