Various plasticizers have been used in polymer electrolyte systems, mainly to enhance the ionic conductivity of the electrolyte. Therefore, in this study, the effects of dimethyl carbonates, DMC plasticizer on the ionic conductivity of poly (methyl methacrylate), PMMA electrolyte film when blended with 50% epoxidized natural rubber and ENR 50 were investigated. Unfortunately, the addition of DMC plasticizer reduced the ionic conductivity of this blend system at any amounts of plasticizer added. In addition, this DMC-plasticized system also exhibited higher activation energy than the unplasticized system. The effects of DMC plasticizer on the conductivity of this electrolyte system were investigated and explained using Field Emissions Scanning Electron Microscope, FESEM and Fourier Transform Infra Red, FTIR Spectrophotometer analyses. From these analyses, it can be concluded that the dielectric constant of a plasticizer is important when dealing with an electrolyte system containing rubber.