The cell structure and interface between cultured cells and a multiwalled carbon nanotube (MWCNT)-coated sponge (MWCNT-coated sponge) were observed by transmission electron microscopy (TEM). Moreover, the atomic structure of MWCNTs that entered the cells was also examined by means of high-resolution TEM (HRTEM). MWCNTs were observed in the cytoplasm, and a few MWCNTs were recognized in the cell nuclei. Those MWCNTs maintained their structure there. Subcellular organelles did not appear to be different from those on the collagen sponge despite the cellular uptake of MWCNTs.