Titanium implant surfaces may serve as attachment substrates for various cell types. Since carbon adsorption on titanium is inevitable, this study examined the negative/positive biological reaction of osteoblasts and fibroblasts on carbon-deposited titanium surfaces. Osteogenic MC3T3-E1 and fibrogenic NIH/3T3 cells were separately cultured on titanium disks on which carbon deposition was experimentally regulated to achieve titanium/carbon ratios of 6.5, 0.02, 0.005, and 0. The initial attachment of cells demonstrated that the quantity of attached osteoblasts on Ti/C (0.005) surfaces was 20% lower than that on Ti/C (6.5) surfaces at 4 h of culture. A 40% reduction in cell attachment at 24 h transferring from Ti/C (6.5) to Ti/C (0.005) surfaces highlighted the negative effect of carbon deposition on osteoblast attachment. However, the initial attachment of fibroblasts, which depended on carbon deposition, increased, and the quantity of cells on Ti/C (0.005) surfaces was almost twice that on Ti/C (6.5) surfaces at 4 h of culture. The levels of common differentiation markers of collagen synthesis were also differentially carbon-dependent as total collagen deposition on Ti/C (0.005) decreased by &gt
30% compared to that on Ti/C (6.5) in osteoblasts after 7 days of culture. In contrast, collagen synthesis in fibroblasts markedly increased as was evident by the increase in carbon deposition. These inverse effects indicate that carbon deposition on a titanium surface would likely be a disadvantage for bone formation, but might represent an effective option for achieving better wound healing and soft tissue sealing around the surface of an implant-neck region. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1869–1877, 2018.