Interfacial localization of conductive fillers in co-continuous polymer blends is an effective method to enhance a conductivity of the composite with low filler content by forming a conductive paths at interfaces. In this study, biodegradable poly(lactic acid) (PLA) was blended with poly(trimethylene terephthalate) (PTT) to make the co-continuous blend. Glycidyl methacrylate (GMA) was grafted on reduced graphene oxide (rGO-GMA) because epoxy group of rGO-GMA was expected to react with both PLA and PTT and localize at interface by two-step blending procedure to make the conductive paths between PLA and PTT. Firstly, rGO-GMA was blended with PTT to make a masterbatch. Then the masterbatch was blended with neat PLA, respectively. From transmission electron microscopy (TEM), it was observed that rGO-GMA localized between PLA and PTT. Moreover, the electrical resistivity of the composite was remarkably improved, compared with neat polymers. Due to the rGO-GMA at the interface between PLA and PTT in PLA/PTT/rGO-GMA blend by two-step blending, it could effectively work for conductive application.