onic conductivity, dielectric and thermal properties of (PEO)12LiBF4 solid polymer electrolyte, dispersed with nanoporous Al2O3 have been studied. Out of seven different compositions studied, the (PEO)12LiBF4 polymer-salt complex showed the highest conductivity with σ25 oC = 8.27 × 10-6 S cm-1. Dispersion of different weight ratio of nano-porous alumina fillers to this electrolyte showed that the composite electrolyte composition with 15 wt. % Al2O3 gave the highest conductivity with σ25 oC = 6.05 × 10-5 S cm-1. The glass transition temperature, Tg decreased from -35.3 oC to -43.2 oC and the PEO crystallite melting temperature, Tm decreased from 64.5 oC to 58.8 oC due to the incorporation of 15 wt. % Al2O3 filler, suggesting that the interaction between the PEO backbone and the Al2O3 filler have affected the main chain dynamics of the host polymer. As the presence of the filler results in an increased conductivity mainly due to an increased amount of amorphous phase in the electrolyte above Tm, another mechanism, directly associated with the filler particles, appears to contribute to the observed conductivity enhancement. A possible mechanism for this could be the creation of additional hopping sites and favorable conducting pathways for migrating ionic species though Lewis acid-base type interactions between ionic species and O/OH sites on the filler grain surface. Results of the dielectric relaxation spectroscopy agree with the suggestion that the increased mobility is largely responsible for the obtained conductivity enhancement caused by the nano- porous filler.