Improving the filtration and biological performances of polymeric membranes has become a major bottle-neck to forward the membrane based separation and purification technologies. Herein, for the first time, we report the usage of aramid nanofiber (ANF) to enhance the ultrafiltration and biological performances of polysulfone (PSf) and polyethersulfone (PES) membranes. ANF is a relatively hydrophilic additive with a water contact angle around 40 degrees however, different from many other hydrophilic or amphiphilic additives, ANF is completely stable and non-dissolvable in water, which makes it an ideal modifier for generating hydrophilic composite membranes. After the addition of ANF, the membranes exhibit more porous structures and enhanced surface hydrophilicity. The flux recovery ratio, protein adsorption and bacterial adhesion tests validate that the ANF modified membranes own improved antifouling properties. Notably, the ANF modified membranes also show improved blood compatibility in terms of limited protein adsorption, suppressed platelet adhesion and activation, inhibited coagulant factors and complementary factors activation. Furthermore, the addition of ANF enables more efficient adsorption of small molecular creatinine toxins during dialysis applications of the composite membranes. In general, this hydrophilic, low-cost, and nanofibrous ANF modifier will be of promising potential for the modification of ultrafiltration membranes and forward their applications in water purification and hemodialysis.