A nanofibrous membrane with a hierarchical structure that was prepared from p-aramid nanofibers via a solvent-induced phase inversion process is reported herein. First, the p-aramid threads were dispersed into and mechanically stirred in a solution of potassium tert-butoxide and methanol for 36 h to yield p-aramid nanofibers. The average length and diameter of the p-aramid nanofibers were > 1.0 mu m and 14.6 +/- 0.7 nm, respectively. Second, nanofibrous membranes were prepared via a 'casting-and-immersion' method in a DMSO/water mixture coagulation bath through a phase inversion mechanism. The pure water flux and bovine serum albumin (BSA) retention ratio of the membranes as well as the membrane-forming mechanism with different preparation parameters, such as the PEG additive dosage, molecular weight of the PEG additive, pre-evaporation time of the liquid film, coagulation bath composition, as well as the concentration of the casting solution, were systematically investigated. The resultant membrane had a highly desirable hierarchical structure, which contains a dense and finely porous barrier layer, as well as a highly porous support layer. This membrane exhibited a high pure water flux and a BSA retention ratio of similar to 852.5 L/m(2) center dot h and 98.7% at an operating pressure of 0.2 MPa, respectively, as well as a high decomposition temperature and tensile strength of 318 degrees C and 17.1 MPa, respectively. The membrane showed good organic solvent resistance even after it had been soaked in a common polar organic solvent for 15 days. Furthermore, the membrane's performances were also extremely stable even with 10 h of heating at 90 degrees C. The membranes prepared in this work may have uses in filters for separations.