Ionic conductivity of polymer electrolytes obtained by complexation of trifluoromethanesulfonic acid (HCF3SO3) (triflic acid) with polyethylene oxide (PEO) has been found to increase with the addition of dimethylacetamide (DMA) as plasticizer. The increase in conductivity has been explained to be due to dissociation of ion aggregates with the addition of plasticizer, which has also been supported by FTIR studies. Plasticized polymer electrolytes have high ionic conductivity but not show better mechanical properties. Nano-sized fumed silica (SiO2) is added to improve its mechanical strength alongwith an increase the ionic conductivity of plasticized polymer electrolytes. Maximum ionic conductivity of plasticized nano-composite polymer electrolytes of 8.14 x 10(-3) Scm(-1) at room temperature has been observed for the composition PEO + 8 wt% HCF3SO3 + 50 wt% DMA + 3 wt% SiO2. X-ray diffraction studies of polymer electrolytes suggests that the amorphous content increases with the addition of plasticizer and nano-filler, which is in agreement with the conductivity results. The small change in conductivity over 30-130 degrees C temperature range suggests that these electrolytes are suitable for their use in device applications like fuel cells, supercapacitors, sensors, separators and other electrochromic devices. DSC/TGA studies show that these nano-composite plasticized polymer electrolytes possess good thermal properties alongwith high conductivity.