It is well known that the reduction of AgBF 4 to silver nanoparticles inevitably occurs over time even under dark conditions. In particular, the reduction rate of AgBF 4 in a polymer/silver salt complex is much faster than for any other silver salt. However, when Al(NO 3 ) 3 was incorporated into a POZ/AgBF 4 complex, the reduction of silver ion was suppressed for more than 14 days. Stable silver ions were confirmed by the separation performance of propylene/propane mixtures over time and by the color change of the POZ/AgBF 4 /Al(NO 3 ) 3 complex. FT-IR and FT-Raman spectroscopy showed that ionic aggregation between the silver ion of AgBF 4 and NO 3 - of Al(NO 3 ) 3 occurred, which was much stronger in intensity than interactions in the POZ/Al(NO 3 ) 3 and POZ/AgNO 3 complexes. This strong aggregation behavior was attributable to a favorable interaction between F − of AgBF 4 and Al 3+ of Al(NO 3 ) 3 , resulting in a weakened interaction between Al 3+ and its counteranions, which was confirmed by XPS.