Synthesis and characterization of composite polymer electrolytes based on lithium bis(oxalato)borate (LiBOB) and a host matrix of nanoparticulate anatase dispersed in phase-separated poly(vinylidenefluoride) (PVdF)-poly(vinylchloride) (PVC) are described. Ethylene carbonate (EC) and diethyl carbonate (DEC) were used as plasticizers in the membranes, and nanoparticulate TiO2 (anatase) was used as the filler. The membranes were characterized by SEM, XRD, and a.c. impedance measurements. A membrane with 2.5 wt% filler exhibited a conductivity of 5.43 x 10(-4) S.cm(-1) at ambient temperature. Filler levels above 2.5 wt% increased the crystallinity of the membranes, rendering them less conducting. Activation energy and coherent length of the composite polymer electrolytes have also been calculated. POLYM. ENG. SCI., 49:2109-2115, 2009. (C) 2009 Society of Plastics Engineers