In this paper, we report that fast evaporation of volatile solvent from cellulose acetate (CA) solution layer containing a proper nonvolatile alcohol can lead to the formation of relatively uniform nanoporous CA membrane. We propose that in the phase separation process, the molecules of the nonvolatile alcohol aggregate to constitute the polymer-lean nuclei (PLN). These PLN exist stably (but not evaporate), grow continuously, and develop finally into the pores on the membrane. Relevant evidences are provided to support the proposed mechanism. This work implies a possible approach to generate uniform nanopores on polymer membrane. (C) 2015 Elsevier By. All rights reserved.