Ultrafine polysaccharide nanofibers (i.e., cellulose and chitin) with 5-10 nm diameters were employed as barrier layers in a new class of thin-film nanofibrous composite,(TFNC) Membranes for water purification. In addition to concentration, the viscosity of the polysaccharide nanofiber coating suspension was also found to be affected by the pH. value and ionic strength. When compared with two commercial UF membranes. (PAN10 and PAN400), 10-fold higher permeation flux with:above 99.5% rejection ratio were achieved by using ultrafine cellulose nanofibers-based TFNC membranes for ultrafiltration of oil/water emulsions. The very high surface-to-volume ratio and negatively charged surface of cellulose nanofibers, which lead to a high virus adsorption capacity as verified by MS2 bacteriophage testing, offer further opportunities in drinking water. applications. The low cost of raw cellulose/chitin materials, the environmentally friendly fabrication process, and the impressive high flux performance indicate that such ultrafine polysaccharide nanofibers-based TFNC membranes can surpass conventional-membrane systems in many different water applications.