This work studies cell viability and cell adhesion on as grown dense films of vertically aligned carbon nanotubes (MWCNT). The MWCNTs were produced by a microwave plasma chemical vapor deposition (2,45GHz) on silicon (Si) and titanium (Ti) surfaces, using a nickel and iron catalyst, respectively. The citotoxicity tests (MTT assay and cellular adhesion) were evaluated by various incubations times with Fibroblast L929 mouse cells. The results show very high cell viability and many layers of cells adhered on the surface formed by the nanotubes tips at films grown on Si surfaces. The MWCNT grown on Ti surfaces presented lower cell viability and a reduced number of cells on the surface formed by the nanotubes tips. The different behavior is most probably related to excess iron contamination present in the case of titanium substrate, while nickel catalyst is probably enclosed by the nanotubes.