Multiwalled carbon nanotubes (MWCNTs) were successfully incorporated in ultrafine cellulose fibers by electrospinning MWCNT-loaded cellulose acetate (CA) solutions, followed by deacetylation of CA to cellulose (cell). The mean fiber diameter reduced from 321 nm of the as-spun fibers to 257 and 228 nm of those with 0.11 and 0.55 wt % MWCNTs, respectively, and became more uniform. Hydrolysis of CA to cell further reduced the mean fiber sizes by another 8-16%. The MWCNTs were observed to be well-aligned along the fiber axes. The MWCNT/cell composite fibers had increased specific surface, from 4.27 m(2)/g to 5.07 and 7.69 m(2)/g at 0.11 and 0.55 wt % MWCNTs, respectively, and much improved water wettability. The mechanical properties of the fibers were also greatly enhanced with increased MWCNT loading levels. The fact that MWCNTs were observed in only about a third of the fibers at a very low 0.55 wt % loading suggests significantly higher tensile strength may be achieved by a further increase in MWCNT loadings.