The correlation between the anions of the ionic liquids of BMIM+BF4-, BMIM+CF3SO3- and BMIM+NO3- in poly(2-ethyl-2-oxazoline)/AgNO3 membranes and reduction of silver ions has been investigated. The anion type negligibly affected the initial separation performances, however it significantly affected the long-term operation stability. Additionally, UV and TEM confirmed the long-term operational stability was strongly associated with the reduction rate of the silver ions. The reduction rate of the silver ions in the polymer/silver salt/ionic liquid complex was observed in following order: BMIM+BF4- > BMIM+CF3SO3- > BMIM+NO3-, suggesting that among the ionic liquids investigated, BMIM+NO3- had the most improved separation performance.