The direct electrospinning of a non-derivatized cellulose (Cs)-chitosan (Ch) composite nanofiber is described for the first time. Either of two cellulose preparations from different sources, i.e., cotton (Cs-C) or bamboo (Cs-B), is fabricated into composite electrospun non-woven fabrics (ESNWs) with Ch using the trifluoroacetic acid-acetic acid mixed solvent. The total concentration of Cs+Ch in the mixed solvent is fixed at 4.0wt.-% with various Cs/Ch weight ratios of 8:2, 5:5 (Figure shows Cs-B/Ch-ESNW), and 2:8, which are fabricated into fine fibers in the Cs/Ch-ESNWs having average diameters mostly <100nm. The treatment of the composite fibers with an alkaline-alcohol solution produces the water-resistant ESNWs, which can retain their fine fibrous network in aqueous environments.