Carbon nanotubes (CNT) is one of the most studied biomaterials, and issues about its cytotoxicity remain. The objective of our study was to investigate the in vitro influence of defective CNT on culture growth and on the formation of mineralized matrix nodules by primary osteoblastic cells grown in plastic or titanium (Ti) surfaces. Cellular viability, alkaline phosphatase activity and formation of mineral nodules were evaluated, besides the CNT characterization tests. The CNT studies showed better cell viability for osteoblasts incubated at stationary phase of culture in the presence of Ti (about 70%), but for the other phases, the cells suffered a significant reduction in viability. A peak of maximum alkaline phosphatase activity in the intermediate stage of growth (14 days of culture), which is characteristic for osteoblasts, was not affected, regardless of the presence of Ti or combination of CNT and Ti. Mineralized matrix nodules grew much more when the cells were incubated with CNT in the last 2 phases than when incubated in the first week, mainly when the cultures were grown on Ti discs. This study provides information for the application of CNT associated or not with Ti in processes of mineralization biostimulation.