Among bone morphogenetic proteins (BMPs), BMP-9 has been described as one with higher osteogenic potential. Here, we aimed at evaluating the effect of BMP-9 on the osteoblast differentiation of cells grown on titanium (Ti) with nanotopography, a well-known osseoinductive surface. MC3T3-E1 cells were grown either in absence or presence of BMP-9 (20 nM) on Ti with nanotopography (Ti-Nano) or machined Ti (Ti-Machined) for up to 21 days to evaluate the gene expression of RUNX2, osterix, osteocalcin, bone sialoprotein, SMAD6 and SMAD4, protein expression of SMAD4, ALP activity and extracellular matrix mineralization. As expected BMP-9 increased osteoblast differentiation irrespective of Ti surface topography; however, the cells grown on Ti-Nano were more responsible to BMP-9 compared with cells grown on Ti-machined. This could be, at least in part, due to the fact that Ti-Nano may act on both ways, by increasing the activation (SMAD4) and decreasing the inhibition (SMAD6) of the signaling pathway triggered by BMP-9, while Ti-Machined only decrease the inhibition (SMAD6) of this pathway. In conclusion, the combination of the osteogenic potential of BMP-9 with the osseoinductive capacity of Ti-Nano could be a promising strategy to favor the osseointegration of Ti implants.