In this study, polymer electrolytes derived from polymethyl methacrylate/50 % epoxidized natural rubber (PE) were successfully prepared. The effects of silicon dioxide (SiO2) (15 nm) and acid modified SiO2 (HCl-SiO2) (15 nm) on the film formation and ionic conductivity of polymer electrolytes were investigated. In samples preparation, SiO2 was used as received. Meanwhile, HCl-SiO2 was prepared by reacting SiO2 with 7 M of hydrochloric acid (HCl) solution. PE, PE filled with SiO2 (PE-SiO2) and PE filled with HCl-SiO2 (PE-HCl-SiO2) electrolytes were prepared by solvent casting method with tetrahydrofuran (THF) as solvent and lithium tetrafluoroborate (LiBF4) as doping salt. The smoothness surface, opacity and agglomeration of PE-HCl-SiO2 film were found in between PE and PE-SiO2. CHNS analysis shows that the percentage of hydrogen in HCl-SiO2 and SiO2 are 0.88 and 2.07 %, respectively. Fourier transform infra-red (FT-IR) analysis confirm that HCl-SiO2 has low number of silanol group (Si-OH) but high number of siloxane group (Si-O-Si) compared to SiO2. Field Emission Scanning Electron Microscopy (FESEM) analysis shows that HCl-SiO2 has smaller size of agglomeration and porosity compared to SiO2. Meanwhile, electrochemical impedance spectroscopy (EIS) analysis shows that the ionic conductivity of PE-HCl-SiO2 is higher than PE but slightly lower than PE-SiO2.