The ion conduction behavior of the plasticized polymer electrolyte based on poly(methylmethacrylate-co-sodium methacrylate) was studied with in-situ FT-IR technique under a de electric field. This study includes a detailed investigation on the various environments of the plasticizer EC in the ionomer electrolyte. The transport of-charge carrier in the ionomer electrolyte was strongly dependent on the ion content of the ionomer and the ionic aggregates were formed in the ionomer electrolyte with around 7 mol% content of the ionomer. From the in-situ FT-IR experiments the transference number could be also calculated.