A new plasticized polymer electrolyte composed of a blend of poly(acrylonitrile-butadiene-styrene) (ABS) and poly(methyl methacrylate) (PMMA) as a host polymer, mixture of ethylene carbonate (EC) and propylene carbonate (PC) as a plasticizer, and LiClO4 as a salt was studied. Owing to the different miscibility of ABS and PMMA with the plasticizer, phase separation takes place in the electrolyte system as revealed from SEM studies. The ionic conductivity of the electrolytes decreased with the increasing ABS/PMMA ratio and increased with the increasing plasticizer content at the LiClO4 content of 15%. Such conductivity behaviour could be explained in terms of the morphology and the thermal characteristics of the electrolytes. The mechanical property of the electrolytes was much improved compared with that of the electrolyte system containing pure PMMA, plasticizer and lithium salt.